(1) Diplomatic Immunity

11. The principle of legal immunity for diplomatic agents is a fundamental principle of national and international law, rightly described in a recent case as “one of the most important tenets of civilised and peaceable relations between nation states”: A Local Authority v AG [2020] EWFC 18; [2020] Fam 311, para 38 (Mostyn J). At the international level the relevant law is contained in articles 1, 22-24, 27-40 and 45 of the Vienna Convention on Diplomatic Relations 1961 (the “Diplomatic Convention”), to which 193 states are parties. Section 2(1) of the Diplomatic Privileges Act 1964 (the “1964 Act”) incorporates these provisions into UK domestic law.

12. As recorded in the fourth recital to the Diplomatic Convention, the purpose of diplomatic privileges and immunities “is not to benefit individuals but to ensure the efficient performance of the functions of diplomatic missions as representing States”. To this end:

1. (i) the premises of the mission are inviolable (article 22);

2. (ii) all correspondence relating to the mission and its functions is inviolable and the diplomatic bag must not be opened or detained (article 27);

3. (iii) the person of a diplomatic agent is inviolable and he shall not be liable to any form of arrest or detention (article 29);

4. (iv) the premises of a diplomatic agent are inviolable, as are his papers, correspondence and (save in cases where he is not immune from civil jurisdiction) his property (article 30);

5. (v) a diplomatic agent enjoys immunity from the criminal jurisdiction and (with limited exceptions) the civil and administrative jurisdiction of the receiving state (article 31(1));

6. (vi) a diplomatic agent is not obliged to give evidence as a witness (article 31(2));

7. (vii) diplomatic immunity may be waived only by the sending state and not by the individual (article 32);

8. (viii) with limited exceptions, diplomatic agents are exempt from all dues and taxes in the receiving state (article 34);

9. (ix) the privileges and immunities enjoyed by a diplomatic agent extend to family members who form part of his household (article 37); and

10. (x) although such privileges and immunities normally cease when the functions of a diplomatic agent have come to an end, immunity continues to subsist with respect to acts performed in the exercise of his functions as a member of the mission (article 39(2)).

(2) Article 31(1)(c)

13. The key provision for present purposes is the exception to immunity from the civil jurisdiction of the receiving state provided for in article 31(1)(c) of the Diplomatic Convention. This exception applies in the case of:

(3) The scope of official functions

14. In Reyes this Court unanimously held that the employment and alleged acts of maltreatment of the claimant by the respondent diplomat were not performed “in the exercise of his functions as a member of the mission” within the meaning of article 39(2). As discussed by Lord Sumption (with whom the rest of the Court agreed on this point), a diplomatic agent's “functions as a member of the mission” in article 39(2) are the same as “his official functions” in article 31(1)(c) and are, in each case, those functions which the diplomatic agent performs for or on behalf of the sending state: see [2019] AC 735, para 20. The acts alleged in Reyes were plainly not done for or on behalf of Saudi Arabia (see para 48); and the same is equally true here.

15. It is not suggested that the alleged acts of Mr Basfar were a “professional” activity. The question is whether they were a “commercial activity exercised” by him within the meaning of article 31(1)(c) of the Diplomatic Convention.

(4) Principles of interpretation

16. The text of an international convention is intended to be given the same meaning by all the states which become parties to it. The provisions of the Diplomatic Convention enacted into UK law by the 1964 Act must therefore be interpreted, not by applying domestic principles of statutory interpretation, but according to the generally accepted principles by which international conventions are to be interpreted as a matter of international law: see Fothergill v Monarch Airlines Ltd [1981] AC 251; Reyes [2019] AC 735, para 10. Those principles are set out in the Vienna Convention on the Law of Treaties 1969 (the “Treaties Convention”).

17. The general rule of interpretation is stated in article 31(1) of the Treaties Convention as follows:

Article 31(3) provides that “[t]here shall be taken into account, together with the context:

18. Article 32 of the Treaties Convention permits recourse to be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31 or if applying article 31 leaves the meaning ambiguous or obscure or leads to a result which is manifestly absurd or unreasonable.

(1) Ms Wong's case

19. The arguments made on Ms Wong's behalf, like the claimant's case in Reyes, have relied heavily on a contention that the facts alleged amount to “trafficking in persons”, as that term is defined in the United Nations Protocol to Prevent, Suppress and Punish Trafficking in Persons Especially Women and Children, supplementing the United Nations Convention against Transnational Organized Crime 2000 (the “Palermo Protocol”). Mr Timothy Otty QC put forward Ms Wong's case in the form of a syllogism:

1. (i) Human trafficking is a commercial activity.

2. (ii) Ms Wong's claim relates to human trafficking (of her by Mr Basfar).

3. (iii) Consequently, her claim relates to a commercial activity allegedly exercised by Mr Basfar and so falls within the exception from immunity provided in article 31(1)(c) of the Diplomatic Convention.

(2) Mr Basfar's case

20. For Mr Basfar, Mr Mohinderpal Sethi QC approached the issue from a different direction. Adopting the reasoning of Lord Sumption's minority judgment in Reyes (on this point), he submitted:

1. (i) The employment of a domestic servant at a diplomat's private residence does not constitute the exercise of a commercial activity by a diplomatic agent within the meaning of the exception.

2. (ii) It makes no difference if the domestic servant is a victim of human trafficking.

3. (iii) Therefore, even if Ms Wong was trafficked by Mr Basfar, he has diplomatic immunity in relation to her claim.

21. Mr Sethi QC also sought to advance an argument not made below that the facts alleged by Ms Wong do not come within the definition of human trafficking set out in the Palermo Protocol. He further submitted that Ms Wong's claim in the employment tribunal for wages and breaches of her employment rights is in any case not “an action relating to” human trafficking. In response, in written submissions filed at the Court's invitation after the hearing, counsel for Ms Wong argued that, even if the facts alleged do not come within the definition of human trafficking, the claim can properly be characterised as relating to (a) forced labour and/or (b) domestic servitude.

(3) Human rights arguments

22. In Reyes the similar allegation of human trafficking made in that case was relied on to argue that the 1964 Act and the Diplomatic Convention should be interpreted to achieve consistency with rules of international law which require states to prevent and provide effective remedies for human trafficking. In particular, reference was made to article 6(6) of the Palermo Protocol, which requires each state party to ensure that “its domestic legal system contains measures that offer victims of trafficking in persons the possibility of obtaining compensation for damage suffered.” A similar obligation is imposed on states which are parties to the Council of Europe Convention on Action against Trafficking in Human Beings 2005 by article 15(3). The claimant also sought to rely on articles 4 and 6 of the European Convention on Human Rights (the “ECHR”). Article 4 of the ECHR prohibits slavery, servitude and forced or compulsory labour. In Rantsev v Cyprus and Russia (2010) 51 EHRR 1, the European Court of Human Rights held that, although not expressly referred to, human trafficking also falls within the scope of article 4 and that member states have positive obligations under article 4 which include an obligation to put in place a legislative and administrative framework to prohibit and punish human trafficking. Article 6 of the ECHR confers a right of access to the courts. The claimant argued in Reyes that the 1964 Act and the Diplomatic Convention must be interpreted in a way which does not place the UK in breach of these international obligations.

23. In Reyes the Court of Appeal gave detailed reasons for rejecting these arguments: see [2016] 1 WLR 1785, paras 35-76. So did Lord Sumption in the Supreme Court: see [2019] AC 735, paras 40-45. In short:

1. (i) Domestic principles of statutory interpretation are not relevant in interpreting the provisions of the Diplomatic Convention incorporated into UK law, which must be given their international meaning (see para 16 above).

2. (ii) There is no inconsistency between the international obligations of the UK to prohibit and create liabilities for human trafficking and the immunity of diplomats in international law from the jurisdiction of the local courts. The position is no different from cases involving torture or war crimes and crimes against humanity, which are contrary to peremptory norms of international law (ius cogens) but where international law jurisdictional immunities nevertheless apply: see Jones v Ministry of the Interior of the Kingdom of Saudi Arabia [2007] 1 AC 270 (torture); Jurisdictional Immunities of the State (Germany v Italy) [2012] ICJ Rep 99 (war crimes).

3. (iii) Restrictions on the right of access to a court which reflect the rules of diplomatic immunity recognised in international law cannot in principle be regarded as disproportionate to the legitimate aim of complying with a state's international law obligations to ensure the efficient performance of diplomatic functions: see most recently London Borough Council v AG [2021] EWHC 1253 (Fam); [2021] Fam 404, para 98.

24. On this appeal counsel for Ms Wong have not pursued the arguments based on UK domestic law principles of statutory interpretation or on articles 4 and 6 of the ECHR which were rejected in Reyes. Despite this, the Special Rapporteur included such arguments in her written intervention. The Court granted the Special Rapporteur permission to do so, but expressly without prejudice to the relevance of those arguments to the issues in the appeal. It is seldom appropriate for an intervener to make submissions on matters which are not in issue between the parties to the appeal. Exceptionally, if there is an important point of law which the parties have overlooked, it may be justifiable to raise it so that the court can consider whether to invite argument from the parties on the point. In this case, however, the decision of Ms Wong's representatives not to renew some arguments rejected in Reyes was plainly deliberate. It is also to be commended. The result of the Special Rapporteur advancing those arguments was that counsel for Mr Basfar understandably felt compelled to respond to them. It is sufficient to say that the Special Rapporteur did not point to any alleged error in the reasoning in Reyes summarised above, and we agree with that reasoning.

25. There is in any case a further, and in our view fatal, objection to the attempt to rely on human rights law to interpret article 31(1)(c) of the Diplomatic Convention, noted by Lord Sumption in Reyes at para 45. This is that the exception to diplomatic immunity created by article 31(1)(c) is not based on whether the relevant activity is contrary to international law or violates human rights. The sole question is whether the activity is “professional or commercial”. Certainly, some commercial activities are contrary to rules of international law, for example dealing in illicit drugs. But the fact that an activity is unlawful has no direct bearing on whether or not it is commercial.

26. In these circumstances we do not find it helpful to begin, as counsel for Ms Wong did in their submissions, with the international definition of human trafficking. We will consider that definition and other international law concepts often grouped under the label of “modern slavery” at a later stage of our analysis. But the critical questions are what is meant by a “commercial activity exercised” by the diplomatic agent and whether the conduct of Mr Basfar alleged in this case falls within that description.

(1) Employment of a domestic worker

27. Applying the general rule of interpretation set out in article 31(1) of the Treaties Convention (see para 17 above), we agree with Mr Basfar's contention that employing a domestic worker does not itself constitute the exercise of a “commercial activity” by a diplomatic agent within the meaning of the exception.

(2) The profit element

39. Article 42 of the Diplomatic Convention states:

In Reyes [2016] 1 WLR 1785, paras 11-12, 16-17, the Court of Appeal agreed with the view of Laws J in Propend Finance Pty Ltd v Sing (1997) 111 ILR 611, 635, that the phrase “professional or commercial activity” is intended to have the same meaning in both article 31(1)(c) and article 42 and that, in the words of Laws J, “the very rationale of article 31(1)(c) is to see to it that no immunity enures for the benefit of a diplomat where for one reason or another his activities do not comply with the article 42 prohibition.” Lord Sumption in Reyes [2019] AC 735, para 21(3), took the same view, which he thought was confirmed by the drafting history of the Diplomatic Convention: see para 38(1). Counsel for Mr Basfar have adopted this analysis.

40. We agree that there is a clear link between the two provisions and that, where a diplomatic agent practises an activity incompatible with his diplomatic status in breach of article 42, article 31(1)(c) ensures that the diplomat will not enjoy immunity from civil actions relating to that activity. To that extent, article 31(1)(c) is clearly intended to complement article 42. We are not persuaded, on the other hand, that article 31(1)(c) goes no wider than article 42. In one respect at least, the scope of article 31(1)(c) is undoubtedly wider, as the exception from immunity in article 31(1)(c) applies (by article 37) to members of the family of a diplomatic agent forming part of his household, whereas the article 42 prohibition does not. Thus, article 42 does not prevent, for example, the spouse of a diplomatic agent from working in paid employment or carrying on a business in the receiving state; yet there is no doubt that the spouse does not have immunity from suit in respect of such activities. The inclusion in article 42 of the words “for personal profit” also indicates that article 42 was not intended to prohibit a diplomat from carrying on a professional or commercial activity on a voluntary basis, for example teaching or helping out in a charity shop for no remuneration; whereas the absence of those words in article 31(1)(c) suggests that a civil claim relating to such conduct would nevertheless fall within the exception from immunity.

41. For present purposes, however, it is unnecessary to decide this point. This is because, as we explain below, we are satisfied that, on the assumed facts, Mr Basfar's exploitation of Ms Wong was undertaken for his personal profit.

(3) Exploitation of a domestic worker

42. The next step in Mr Basfar's argument is to contend that, seeing as the ordinary employment of a domestic worker by a diplomatic agent does not constitute the exercise of a commercial activity within the meaning of article 31(1)(c), the same must be true where a domestic worker is trafficked and exploited by a diplomat.

43. It is here that we part company with the argument. We cannot accept that exploiting a domestic worker by compelling her to work in circumstances of modern slavery is comparable to an ordinary employment relationship of a kind that is incidental to the daily life of a diplomat (and his family) in the receiving state. There is a material and qualitative difference between these activities. Employment is a voluntary relationship, freely entered into and governed by the terms of a contract. Subject to contractual provisions about notice, employees are free to leave when they please, and cannot be compelled to stay by injunction even if they leave in breach of contract. By contrast, the essence of modern slavery is that it is not freely undertaken. Rather, the work is extracted by coercion and the exercise of control over the victim. This usually involves exploiting circumstances of the victim which make her specially vulnerable to abuse. Those constraints generally make it impossible or very difficult for the worker to leave. That is why, on the assumed facts, we describe Ms Wong's departure from service with Mr Basfar as an “escape”.

(4) Making a personal profit

52. So far we have been concentrating on the factors which enabled Mr Basfar to exercise a very high degree of control over Ms Wong's person and labour and hold her in a form of modern slavery. But what is also critical for present purposes is how Mr Basfar exploited such control for personal profit. This is not only because of the potential effect of article 42, but also because personal profit is an element of what may make a particular activity commercial. On the assumed facts, Mr Basfar and his family enjoyed the benefit of Ms Wong's services for almost two years, initially for a fraction of her contractual entitlement to wages and latterly for no pay at all. That was a substantial financial benefit. The deliberate and continuing course of conduct by which that benefit was gained is in our view properly characterised as the exercise of a commercial activity.

53. Counsel for Mr Basfar disputed this on the basis that no money changed hands. According to this argument, if Mr Basfar had made Ms Wong's services available to someone else in return for payment, the commercial activity exception would have applied; but because he and his family enjoyed the benefit of her services themselves, it does not. This argument seems to us unsustainable as a matter both of law and economics. Any realistic form of economic measurement, not to say system of taxation, takes account of benefits in kind which have monetary value. If, for example, as a term of her employment a company executive is provided with the free use of a car and chauffeur, she enjoys an economic benefit which can be taxed and fairly valued at what it would cost to purchase this service in the market. In the same way the monetary value of services derived from forced domestic labour can be measured as the difference between the amount for which the worker would willingly have provided the services or for which equivalent services could have been purchased in the labour market and the amount of money, if any, and other emoluments actually paid for them.

54. This is the basic methodology used by the International Labour Office (ILO) to estimate profits from forced labour in domestic work. The ILO was originally created as part of the Treaty of Versailles in 1919 and is now an agency of the United Nations with 187 state members. As discussed in the ILO report “Profits and Poverty: the economics of forced labour” (2014), p 25:

55. In the present case an obvious starting-point for calculating the profits made by Mr Basfar from Ms Wong's labour on the assumed facts is to compare the amount which Mr Basfar agreed in her contract of employment to pay her with the amount actually paid. That is only the starting-point, however, as the contract stated that Ms Wong would work eight hours a day, with one day off each week and one month off each year, whereas she was allegedly made to work some 12½ hours each day, with no days off and no annual leave, in abusive conditions. The cost of purchasing an equivalent service in the labour market would be prohibitive, if anyone could be found who was willing to provide it at all. In reality, an equivalent service would have required two employees, working in shifts.

56. On any fair view of the matter, Mr Basfar has on the assumed facts made a substantial financial gain from his exploitation of Ms Wong's labour, albeit not in cash but in money's worth. The exploitation has been a systematic activity carried on over a significant period. It is accurately described as a commercial activity practised for personal profit.

57. That conclusion is confirmed by recalling the rationale for construing the words “commercial activity exercised” by the diplomatic agent as excluding a contract for ordinary domestic services, in contrast to the meaning given to similar words in the context of state immunity. That rationale is the need to protect diplomats and their families from hindrance in going about their daily lives in the receiving state. It would be not merely wrong but offensive to suggest that conduct of the kind disclosed by the assumed facts of this case is incidental to daily life, let alone the daily life of an accredited diplomat. Compelling a migrant domestic worker to provide her labour in circumstances of modern slavery cannot reasonably be likened to paying for dry cleaning or ordinary domestic help. Unlike such day-to-day living services, such exploitation is an abuse of the diplomat's presence in the receiving state and falls far outside the sphere of ordinary contracts incidental to the daily life of the diplomat and family members which the immunity serves to protect.

(5) The travaux préparatoires

58. It is not, in our view, necessary in this case to have recourse as a supplementary means of interpretation (pursuant to article 32 of the Treaties Convention) to the preparatory work for the Diplomatic Convention. However, none of the extensive references made by counsel for Mr Basfar to the preparatory work contradicts our conclusions resulting from the application of article 31 of the Treaties Convention.

59. The discussion at the ninth session of the International Law Commission to which Lord Hamblen and Lady Rose refer at para 116[9] of their judgment about unfair dismissal of domestic servants shows that the delegates did not accept a proposal that there should be an exception to immunity from civil jurisdiction for ordinary employment disputes. There would have been no need for this proposal if such disputes fell within what became article 31(1)(c). That is consistent with our conclusion that employing a domestic servant is not itself a “commercial activity” exercised by a diplomatic agent within the meaning of article 31(1)(c). None of the preparatory work cited to us, however, addressed the question whether a diplomatic agent should enjoy immunity from the civil jurisdiction of the receiving state in an action relating to enslavement or exploiting forced labour for financial gain.

60. In Reyes, at para 38, Lord Sumption extracted from his examination of the drafting history the point that the activities intended to be covered by article 31(1)(c) (and article 42) were “activities involving the assumption by a diplomatic agent of a dual status, by which incompatible occupations were being pursued by the same person.” The expression “dual status” is not used in any of the material to which Lord Sumption referred, but we agree with him that a theme of the preparatory work mentioned by him was that engaging in a commercial activity outside the diplomat's official duties would be inconsistent with the dignity of a diplomatic agent. For example, Lord Sumption quoted, at para 36, the report to the General Assembly on the tenth session (ILC Yearbook 1958, Vol II, p 98, Commentary (7)) which commented on what became article 31(1)(c) in the following terms:

61. This reasoning accords with our view that exploiting the labour of a domestic worker for financial gain is a commercial activity exercised by the diplomatic agent outside his official functions. Manifestly, such an activity is wholly inconsistent with the position (and dignity) of a diplomatic agent. It is also a possible consequence of engaging in the activity that the agent would be declared persona non grata. Nor if such cases occur is there a good reason to deprive the victims of such exploitation of their ordinary civil remedies. As discussed above, the reason why the normal employment of a domestic worker falls outside the scope of article 31(1)(c) is because it is an activity that is incidental to the ordinary conduct of daily life, which is not itself a “commercial activity” and for which personal immunity is needed to ensure the efficient performance of the functions of diplomatic missions. The same cannot be said about the activity of profiting from the forced labour of a domestic worker who is held in a state of servitude.

(6) The rate of remuneration argument

62. Although it did not convince the majority of this Court, the argument which chiefly led two Justices and the Court of Appeal in Reyes to express the view that exploiting a domestic servant is not a commercial activity was that the answer to this question cannot depend on the rate of remuneration which the individual is paid. In the Court of Appeal Lord Dyson MR said, at para 34: “The fact that an employer derives economic benefit from paying his employee wages that are lower than the market rate does not mean that he is engaging in a commercial activity.” To similar effect, in his minority judgment in the Supreme Court, at para 46, Lord Sumption said that “the employment of a domestic servant to provide purely personal services cannot rationally be characterised as the exercise of a commercial activity if she is paid less than the going rate or the national minimum wage, but not if she is paid more”.

63. These observations are clearly correct. It could not rationally be said that the defining characteristic of slavery - whether in its traditional or modern form - is that a slave does not receive the national minimum wage or the market rate of remuneration for his services. That would be like saying that the essential difference between a prisoner and a free person is that the rate of pay for prison work is less than the individual could earn in the outside world. While true, it misses the critical distinction - which is between freedom and captivity. There are political and economic theorists who argue that ordinary employment relationships involve the exploitation of labour - the most famous example being Marx's theory of the appropriation of “surplus value”. But such arguments command no general consensus. What is internationally recognised is the distinction between the voluntary exchange of labour for reward on the one hand and, on the other hand, work exacted through coercion in the form of slavery, servitude and forced or compulsory labour.

(7) “Evolutionary” interpretation

64. A question addressed in argument on the present appeal is whether the language of article 31(1)(c) should be given an “evolutionary” interpretation which takes account of circumstances as they are now or a “static” interpretation which takes account only of circumstances which existed at the time when the Diplomatic Convention was concluded in 1961. This is itself a question of interpretation to be answered by applying articles 31 to 33 of the Treaties Convention. As with domestic legislation, where a treaty is likely to remain in force for a long period of time, it is generally reasonable to presume that the parties intended its language to be interpreted and applied in the light of the circumstances which exist at the time when it is being applied. This presumption is particularly strong where the words used are general or vague and refer to concepts that are fluid and may naturally be expected to alter over time. As the International Court of Justice said in its judgment of 13 July 2009 in Dispute regarding Navigational and Related Rights (Costa Rica v Nicaragua) [2009] ICJ Rep 213, para 66:

65. In the Navigational Rights case it was argued that the term “comercio” (commerce) in a treaty made between Costa Rica and Nicaragua in 1858 did not encompass transporting passengers in a river boat for profit on the ground that such an activity did not fall within the scope of what was commonly called “commerce” at that time. Applying the general presumption expressed in the passage quoted above, the International Court of Justice held that, “even assuming that the notion of ‘commerce’ does not have the same meaning today as it did in the mid-nineteenth century, it is the present meaning which must be accepted for purposes of applying the treaty”: para 70.

(8) Developments of international law

66. The International Court of Justice also noted in the Navigational Rights case, at para 64, that, where the meaning of a term used in a treaty is capable of evolving, and is not fixed once and for all, this enables allowance to be made for “among other things, developments in international law.”

67. The principle that developments in international law since the conclusion of a treaty should be taken into account in interpreting its terms is not only supported by the general presumption in favour of evolutionary interpretation; it is also required by article 31(3)(c) of the Treaties Convention (quoted at para 17 above). In terms of structure, article 31 progresses from terms to context, through any agreements at the time of conclusion of a treaty, to subsequent agreements, subsequent practice, and thence to relevant rules of international law. The juxtaposition, in particular, in article 31(3) of the obligations to take into account (a) subsequent agreements, (b) subsequent practice and (c) “any relevant rules of international law applicable in the relations between the parties” logically indicates that developments in international law subsequent to the conclusion of the treaty are included: see Gardiner, Treaty Interpretation, 2nd ed (2015), pp 290, 298. This also reflects how article 31(3)(c) has been understood and applied in case law: see eg the decisions referred to in A v Secretary of State for the Home Department (No 2) [2005] UKHL 71; [2006] 2 AC 221, para 29, and Rantsev v Cyprus and Russia (2010) 51 EHRR 1, para 274, which take this for granted.

(9) The relevance of developments in international law about modern slavery

68. Lord Wilson in his judgment in Reyes, at para 67, said he was “persuaded that, when agreeing to the terms of the [Diplomatic] Convention, the parties would have rejected any suggestion that the proceedings brought by Ms Reyes related to any commercial activity exercised by Mr Al-Malki”. He nevertheless considered that the meaning of article 31(1)(c) may have developed over the subsequent 56 years in accordance with the development of international law over this period, “in particular the emergence of an international prohibition against trafficking”.

69. Lord Wilson did not explain why he thought that the parties to the Diplomatic Convention would have rejected any suggestion that the proceedings in Reyes fell within article 31(1)(c). For our part, we see no reason to draw such an inference. But we also think that it is addressing the wrong question. In deciding whether the proceedings in Reyes or in the present case fall within article 31(1)(c), the relevant question is not whether the parties to the Diplomatic Convention, if informed of the facts of these cases, would have thought that they fell within article 31(1)(c). It is whether, on the proper interpretation of the text which the parties adopted, the proceedings fall within the meaning of that provision. To answer the latter question, the court must ascertain the common intention of the contracting parties. But the process of identifying this intention is not one of trying to divine what was inside the minds of the parties’ representatives when they negotiated or signed the treaty (let alone what would then have been inside their minds if they had been confronted with a question they did not in fact consider). It is simply a process of applying articles 31 to 33 of the Treaties Convention. In the words of the International Law Commission, those provisions codify “the means of interpretation admissible for ascertaining the intention of the parties”: ILC Yearbook 1966, Vol II, pp 218-19, Commentary (5). Hence as it is put by one commentator, the “intention of the parties” is:

See Bjorge, The Evolutionary Interpretation of Treaties (2014), p 122; and also Gardiner, Treaty Interpretation, 2nd Ed (2015), p 467.

70. Our interpretation of article 31(1)(c) does not assume or assert that the meaning of the words “commercial activity exercised by a diplomatic agent” has changed materially since the Diplomatic Convention was concluded in 1961. We see no reason to suppose that it has. But nor in our view is it relevant to undertake a historical inquiry into what the words meant in 1961 and whether or how their meaning and content has evolved since then. All that matters for the purpose of this appeal is what meaning should be given now to the terms of article 31(1)(c) applying the principles of interpretation codified in articles 31 to 33 of the Treaties Convention.

71. For reasons already given, we do not consider that international prohibitions against trafficking or other practices similar to slavery are of any direct relevance to that question. As we have emphasised in commenting on the human rights arguments advanced by the Special Rapporteur, the fact that an activity is illegal under international law or violates human rights does not make it a “commercial activity”. Nor do we suggest that the adoption of international measures during the last 60 years to combat human trafficking and other forms of modern slavery and to secure rights of compensation for victims has somehow caused such activities to become “commercial activities”. If there is a causal connection, it is the other way round. The adoption of such measures may reflect increased prevalence and international awareness of such forms of exploitation of human beings for profit, as global migration has surged and the world has become more inter-connected. An analogy might be drawn with money laundering. Money laundering undoubtedly took place 60 years ago. But its scale, international awareness of it and the measures taken to combat it have grown immensely in the period since then; and whatever the position might have been in 1961, it seems certain that a diplomat who profits by engaging in money laundering would today be regarded as exercising a commercial activity.

72. In interpreting and applying article 31(1)(c) of the Diplomatic Convention, the only relevance of international law regarding trafficking and other forms of modern slavery, as we see it, is indirect. The critical distinction is between: (1) ordinary domestic employment arrangements which are incidental to the daily life of a diplomat in the receiving state and do not fall within article 31(1)(c); and (2) exploitation of a domestic worker for profit which amounts to a “commercial activity” when practised by a diplomatic agent. We recognise that the distinction is not always a clear one. But that does not make it any less real. On any view there is a fundamental factual as well as moral difference between voluntary employment and slavery and between ordinary domestic service and domestic servitude. To draw the distinction, criteria are needed; and to draw the distinction in interpreting and applying an international convention, it is appropriate to derive those criteria from rules of international law applicable in the relations between the parties. This is the respect, and in our view the only respect, in which rules of international law relating to trafficking and other contemporary forms of slavery are relevant. For this purpose, for the reasons indicated at paras 66-67 above, it is the present rules of international law to which it is necessary to have regard.

(1) Slavery

75. The Convention to Suppress the Slave Trade and Slavery 1926 (the “1926 Slavery Convention”) defines slavery, in article 1(1), as “the status or condition of a person over whom any or all of the powers attaching to the right of ownership are exercised”. This represents the classic definition of slavery in international law and is reproduced, in substance, in both the Supplementary Convention on the Abolition of Slavery, the Slave Trade, and Institutions and Practices Similar to Slavery 1956 (article 7), and the definition of “enslavement” in article 7.2(c) of the Statute of the International Criminal Court 1998.

76. The powers attaching to a right of ownership include the power to sell or otherwise transfer ownership and to use what is owned as a possession, like livestock or furniture. Such “chattel slavery” of human beings is nowadays rare, but the language of the definition, with its reference to “any” of the powers attaching to the right of ownership, permits a more expansive interpretation. Thus, according to a report commissioned by the United Nations:

See Abolishing Slavery and its Contemporary Forms, Office of the United Nations High Commissioner for Human Rights (2002), para 21.

(2) Forced Labour

77. In the process of adopting the 1926 Slavery Convention, the Assembly of the League of Nations passed a number of resolutions, including one which effectively requested the ILO to take over responsibility for addressing forced labour, including “the best means of preventing forced or compulsory labour from developing into conditions analogous to slavery”: League of Nations, Doc A.104.1926.VI, p 3. In 1930 the ILO adopted the Convention Concerning Forced or Compulsory Labour (No 29), which has been ratified by 179 states. Article 2(1) of this convention defines “forced or compulsory labour” as “all work or service which is exacted from any person under the menace of any penalty and for which the said person has not offered himself voluntarily”.

78. Guidance given by the ILO supervisory bodies has helped to clarify each of the two elements of this definition: see eg ILO, “A Global Alliance against Forced Labour” (2005), paras 14-15 and Box 1.1. This guidance explains that the “menace of any penalty” can take many different forms. Arguably, its most extreme form involves physical violence or restraint. There can also be subtler forms of menace, sometimes of a psychological nature. Situations examined by the ILO have included threats to denounce victims to the police or immigration authorities when their employment status is illegal. Other penalties can be of a financial nature, including the non-payment of wages. Indicators that the work is not being performed voluntarily include physical confinement in the work location, deception or false promises about types and terms of work, retention of identity documents and withholding and non-payment of wages.

(3) Servitude

79. Unlike slavery and forced labour, the concept of servitude is not defined in an international convention, though it is used in a number of international instruments including the Universal Declaration of Human Rights adopted by the United Nations General Assembly in 1948, which states in article 4 that “no one shall be held in slavery or servitude”. The term “servitude” is generally understood to refer to a form of exploitation which lies on a scale of gravity or severity between slavery and forced labour and involves coercion. Thus, the US Supreme Court has interpreted the phrase “involuntary servitude”, prohibited by the Thirteenth Amendment to the Constitution, to mean “compulsion of services through the use or threatened use of physical or legal coercion”: see United States v Kozminski, 487 US 931 (1988), p 945. The European Court of Human Rights has held that, in article 4 of the ECHR, “servitude” means an obligation to provide one's services that is imposed by the use of coercion: Siliadin v France (2006) 43 EHRR 16, para 124. The Court has further described servitude as “aggravated” forced or compulsory labour, distinguished by the fact or perception that it is impossible for the individual concerned to change her situation: CN and V v France (Application No 67724/09), 11 October 2012, paras 90-91; Chowdury v Greece (Application No 21884/15), 30 March 2017, para 99.

80. To similar effect, a definition of “servitude” included in the seventh revised draft of the Palermo Protocol, though not in the final text, defined it as:

(4) Human trafficking

81. In contrast to slavery and forced labour, international consensus on a definition of human trafficking is much more recent and was only arrived at in 2000 with the adoption of the Palermo Protocol, to which there are now 178 state parties. Article 3 of the Palermo Protocol defines “trafficking in persons” as meaning:

“Exploitation” is stated to include:

Article 4(a) of the Council of Europe Anti-Trafficking Convention on Action against Trafficking in Human Beings (2005) defines “trafficking in human beings” in similar terms.

82# The definition of human trafficking has three elements:

1. () the act: recruitment, transportation, transfer, harbouring or receipt of persons;

2. () the means (by which the act is done): threat or use of force, coercion, abduction, fraud, deception, abuse of power or vulnerability, or giving or receiving payments or benefits to a person to achieve the consent of a person who has control of the victim; and

3. () the purpose: exploitation, which includes the purpose of forced labour or slavery or servitude.

(5) Is this a case of modern slavery?

83. The application of these concepts to the facts of this case was not the subject of analysis in the proceedings below. Ms Wong's ET1 claim form in the employment tribunal complied with the time-honoured rule that a party must plead the material facts alleged and not their legal consequences. Apart from asserting that Ms Wong “is a victim of trafficking, who was exploited by [Mr Basfar] and his family”, no reference was made to the legal characterisation of her alleged treatment.

84. For the purpose of Mr Basfar's application to strike out the claim on the grounds of diplomatic immunity, the parties agreed that the question for the tribunal was “whether the respondent's employment of the claimant as a domestic servant (in assumed circumstances of modern slavery) was a commercial activity exercised by the respondent outside his official functions”: see para 15 of the tribunal's judgment. The employment judge answered this question in the affirmative, on the ground that this is what the majority of the Supreme Court would have decided in Reyes if they had been required to determine this question. In the Employment Appeal Tribunal, Soole J reached a contrary conclusion essentially on the basis that he should follow the clear view expressed by the Court of Appeal and the minority of the Supreme Court in Reyes (on this point) in preference to the more tentative view expressed by the majority of the Supreme Court. In neither judgment was there any substantive consideration of whether the facts alleged amount to any of the various forms of modern slavery.

85. On the appeal to this court counsel for Ms Wong maintained that she is a victim of human trafficking and that she was exploited in the UK by being held by Mr Basfar in domestic servitude. Mr Otty QC focused on the allegation of trafficking and took the position that he did not need to rely on the concept of forced labour. He submitted that keeping Ms Wong in domestic servitude amounted to “harbouring” her within the meaning of the Palermo Protocol definition of trafficking.

86. For Mr Basfar, Mr Sethi QC submitted that Ms Wong should not be allowed on this appeal to rely on factual allegations not pleaded in her claim form. For example, Ms Wong's written case mentions allegations that her passport was held by Mr Basfar and that she was threatened with arrest if she ran away. Those allegations are not pleaded. Nor is the fact that, since the Court heard oral argument, the Home Office has issued a “conclusive grounds” decision finding that Ms Wong was a victim of modern slavery - a matter on which counsel for Ms Wong have also sought to rely in their written submissions filed after the hearing. We agree with the submission that this Court should determine the appeal on the same agreed factual basis as the tribunals below. We have therefore not included in our summary of the facts or taken into account in our assessment any factual allegations other than those pleaded.

87. Mr Sethi QC also submitted that the facts pleaded by Ms Wong do not amount to trafficking within the international definition. The high point of this argument is that, although Ms Wong asserts in her claim form that she is a “victim of trafficking” and alleges that she was brought from Saudi Arabia to continue working for Mr Basfar here and was subjected to exploitation by Mr Basfar and his family in the UK, she does not expressly allege that she was trafficked to the UK for the purpose of exploitation. Although not expressly stated, this is, however, clearly implicit in the allegations made and is certainly an inference capable of being drawn from those allegations. We see no merit in the suggestion that the claim form is defective for this reason.

(6) The question of taxonomy

96. It is not, however, in our view necessary to resolve this difficult issue, for two reasons. The first is that, on the assumed facts, Mr Basfar was plainly involved in trafficking Ms Wong, regardless of whether, strictly construed, trafficking ceases (as is sometimes said) at the door of the workhouse. He clearly played a principal part in her recruitment, transport and receipt, using the prohibited means and for the purpose of her exploitation. Secondly and more importantly, our conclusion that his exploitation of her was a commercial activity does not depend upon which particular manifestation of modern slavery may best describe his conduct, using the classification to be derived from international Conventions. It is apt to bear in mind this observation of Gleeson CJ in the High Court of Australia in Queen v Tang [2008] HCA 39, para 29:

97. it is sufficient that Mr Basfar's treatment of Ms Wong, on the assumed facts, amounted to a form of modern slavery, whether it was forced labour, servitude or trafficking. This shows that the relationship between them was not that of employment freely entered into, so as to be an ordinary part of Mr Basfar's daily life in the UK as a resident diplomat. And it shows that his conduct amounted to a commercial activity practised (in so far as it matters) for personal profit.

(7) Does the claim “relate to” the alleged commercial activity?

98. It seems to us that the somewhat single-minded focus by the claimants in this case and in Reyes on the term “human trafficking” to describe the matters complained of has had the effect of diverting attention from the substance of the claims. Focusing on trafficking is open to the objection that the alleged trafficking of the claimant was not itself a cause of loss to her or profit to the respondent, as any such loss and corresponding profit were the result of exploitation at the claimant's place of work and not of the process by which she came to be there. On that basis it might be said that, on the facts alleged, any acts of trafficking were not themselves a commercial activity exercised by the respondent; nor do the claims “relate to” trafficking, as they are founded on the alleged exploitation of the claimants while they were working in the UK and not on the process by which they travelled to their place of work.

99. There is some force in those objections when the emphasis is placed on the concept of human trafficking, particularly if, as on one interpretation of the Palermo Protocol, trafficking ends where the exploitation which is its purpose begins. But, on a proper analysis, the allegation of human trafficking is not essential to the claims made. The gravamen of Ms Wong's claim is that she was exploited by being forced to work for Mr Basfar in the UK in circumstances of modern slavery. The case that the exploitation of her labour amounted to a commercial activity would be just as cogent if Ms Wong had already been resident in the UK before working for Mr Basfar and had become an employee of Mr Basfar in the UK freely but he had then treated her in the manner alleged after she entered his service. Conversely, if Mr Basfar had engaged in trafficking by transporting Ms Wong to the UK using deception or coercion for the purpose of exploitation but had then changed his mind and employed her on a regular and voluntary basis, a claim for breach of her contract of employment would not, as it seems to us, fall within the article 31(1)(c) exception. On the facts alleged, the main relevance of the process by which Mr Basfar arranged for Ms Wong's transfer to the UK to work for him (which amounted to trafficking under any interpretation of the Palermo Protocol) is that it is an important part of the background which serves to explain how Ms Wong came to be in a position of special vulnerability to his exploitation of her while in his domestic service.

100. In cases of the present kind the forms of modern slavery primarily relevant, in our view, are likely to be forced labour and servitude (which, as noted above, can be seen as an “aggravated” form of forced labour). It is those international law concepts which provide appropriate criteria for distinguishing between, on the one hand, the voluntary employment of a domestic worker which is an ordinary incident of living in the receiving state and, on the other hand, the exploitation of a domestic worker which is properly characterised as a commercial activity for the purpose of article 31(1)(c) of the Diplomatic Convention. The assumed facts of the present case make it a paradigm example of domestic servitude.

(8) Jurisdiction of the employment tribunal

103. A further point made on behalf of Mr Basfar is that an employment tribunal can only compensate a claimant for claims that it has jurisdiction to hear and such claims do not include an action for trafficking. The same point could be made about claims for compensation for subjection to servitude or forced labour, which equally are not claims that an employment tribunal has jurisdiction to determine.

104. Ms Wong is not, however, claiming compensation for violation of her human rights through being trafficked or held in servitude or required to perform forced labour. Those concepts are relevant only to rebut Mr Basfar's plea of diplomatic immunity. There is no doubt that a court or tribunal has power to decide whether it has jurisdiction to hear a claim. To decide whether or not the plea of immunity from the jurisdiction of the English courts is well founded, it is necessary to determine whether Ms Wong's claim is an action “relating to” a commercial activity exercised by Mr Basfar outside his official functions. In their ordinary meaning, the words “relating to” in article 31(1)(c) require only that there should be a significant connection between the subject matter of the action and the commercial activity exercised by the diplomatic agent, and not that the facts relied on to establish that the relevant activity is “commercial” should be limited to those which need to be proved as ingredients of the claimant's causes of action. Such a connection is clearly present on the assumed facts of this case, as Ms Wong's allegations of unlawful deductions from wages and failures to comply with the law relating to working time and the national minimum wage arise directly from, and are part of, the exploitative conduct which is alleged for the purpose of rebutting the plea of immunity to constitute a commercial activity.

(9) The argument in terrorem

105. Finally, we should notice an argument advanced on behalf of Mr Basfar that, if trafficked domestic workers who have been forced to work for a diplomat in circumstances of modern slavery are allowed to make a civil claim in an employment tribunal for wages wrongly withheld, British diplomats abroad might be exposed to retaliatory measures. There are two problems with this argument. First, it is difficult to see how such a risk, even if genuine, can affect the meaning of the phrase “commercial activity” in article 31(1)(c). Second, there is no evidence to support the existence of such a risk.

106. If the UK Government had considered this to be a real concern, it is to be expected that it would have intervened in these proceedings to say so. The Secretary of State for Foreign, Commonwealth and Development Affairs has not intervened on this appeal but did intervene by way of written submissions in the proceedings before the Court of Appeal and the Supreme Court in Reyes. In that intervention all that was said on this subject was that the court should bear in mind that, if the protection granted by the Diplomatic Convention is eroded or restricted in this jurisdiction, then the same limitations may well be applied to UK diplomats abroad. Such reciprocity is naturally to be expected. It was not, however, suggested by the Secretary of State - and we see no reason to suppose - that the absence of immunity during, as well as after, a diplomat's posting for an employment claim brought by a domestic worker who claims to have been trafficked and held by the diplomat in conditions of modern slavery would impede the conduct of British diplomacy. It is difficult to see how the theoretical possibility of such a claim could be thought to involve an unacceptable interference with diplomatic functions any more than, for example, exposure to the possibility of a civil action alleging participation in commercial fraud, which would on any view fall within the commercial activity exception.

(1) Normal employment as “commercial activity”

114. It now seems to be beyond doubt that the normal employment of a domestic worker in the diplomatic household does not amount to the exercise of a commercial activity on the part of the employer. This issue was considered in detail by Lord Dyson MR in Reyes when it was argued on behalf of the claimant that normal employment was also covered by the article 31(1)(c) exception. He examined the ordinary meaning of the phrase and concluded that as a matter of ordinary language, a contract for the provision of services which are incidental to family or domestic daily life is not “commercial activity”: para 14 of the Court of Appeal's judgment in Reyes. This view was confirmed by the context of the phrase, in particular the link with article 42. As to the object and purpose of the phrase, it was clear from the drafting history and the travaux préparatoires to which Lord Dyson referred that the participants in the Vienna Conference: (i) did not consider that contracts of employment for the provision of domestic services at a mission were already included within the concept of “professional and commercial activities”; and (ii) did not favour enlarging the scope of the exception to a diplomatic agent's immunity to include such contracts of employment. Lord Dyson concluded:

115. We agree with Lord Dyson that the signatories to the Diplomatic Convention were clearly aware that domestic servants were employed in diplomatic residences. Article 1(g) defines “members of the service staff” as members of the staff of the mission in the domestic service of the mission; a “private servant” is defined in article 1(h) as a person who is in the domestic service of a member of the mission and who is not an employee of the sending State. These definitions are important because other provisions of the Diplomatic Convention confer advantages on those falling within those definitions. According to article 37(3), members of the service staff of the mission who are not nationals of or permanently resident in the receiving State shall enjoy immunity in respect of acts performed in the course of their duties. Domestic workers can claim exemption from dues and taxes on the payments they receive by reason of their employment and the exemption from social security provision. Private servants also enjoy certain privileges; see article 37(4).

116. We were also taken to extensive travaux préparatoires. These reveal that there was discussion about the role of domestic staff in the context of considering how far they should share the immunities of the diplomatic family they were serving. Beyond that, it appears that there was no intention to exempt employment issues generally from the civil immunity jurisdiction. The Yearbook of the International Law Commission for 1957, Vol I records the discussions of the ninth session considering the draft codification of the law relating to diplomatic immunity in May 1957. The issue of unfair treatment of domestic servants was raised as a possible additional exception to immunity from jurisdiction by the Yugoslav delegate raising a point that had been put to him by the Yugoslav trade unions. He suggested that some case law suggested that where diplomatic agents enter into contracts with domestic servants, they thereby accepted the jurisdiction of the courts to deal with labour questions. He went on: (p 95 of the 402nd meeting on 22 May 1957)

117. Mr Sandström, the Special Rapporteur, agreed that diplomatic immunity “was often a source of inconvenience” but this was not “so great as to warrant making an exception to the rule”.

118. Lord Sumption in Reyes also emphasised the importance of considering reciprocity when construing the Diplomatic Convention articles:

(2) Diplomatic immunity and egregious conduct by the diplomatic agent

119. There are many instances in the travaux préparatoires where the conference delegates discuss abuses of immunity by diplomatic agents. The choice whether to lift or retain the immunity against claims is nothing to do with the disapproval or acceptability of such conduct. On the contrary, the discussions on the draft at the conference frequently refer to the abuses of privilege that caused public protest in the delegates’ home countries. There was considerable debate about a proposal from the Netherlands to include a separate lifting of immunity for civil liability for car accidents, particularly since the diplomat was likely to be insured: see p 171 of the UN Conference on Diplomatic Intercourse and Immunities in spring 1961 Vol I. But despite such abuses there has been no revision or cutting back of the protection afforded to diplomats from intrusive investigations into their non-commercial life. This was explained by Professor Denza in the Introduction to her work Diplomatic Law: Commentary on the Vienna Convention on Diplomatic Relations, 4th ed (2016) (“Professor Denza's Commentary”). She describes the rules protecting the sanctity of ambassadors and enabling them to carry out their functions as “the oldest established and the most fundamental rules of international law” forming “a cornerstone of the modern international legal order”. She went on:

120. Mr Otty QC drew our attention to the preamble of the Diplomatic Convention which states that the purpose of the privileges and immunities conferred by the text “is not to benefit individuals but to ensure the efficient performance of the functions of diplomatic missions as representing States”. He asked how could it be said that the treatment alleged by Ms Wong promoted the efficient performance of Mr Basfar's functions? We do not regard that as a legitimate approach to construing the scope of the exception in article 31(1)(c). The preamble is intended to express the underlying purpose of the Diplomatic Convention, but it cannot be relied on to restrict the extent of the diplomatic immunity to cover only those activities which might be said to increase their efficiency. We agree with Lord Sumption in Reyes at para 12(3) that:

121. Thus, for example, article 41(3) provides “The premises of the mission must not be used in any manner incompatible with the functions of the mission as laid down in the present Convention or by other rules of general international law or by any special agreements in force between the sending and the receiving State.” But that has not been relied on to argue that if the premises are being used in an incompatible manner, that can affect the scope of the immunities because the misconduct does not promote the efficient running of the mission. Conversely, the immunity is lifted by the other paragraphs of article 31 in.respect of activities which could not generally be regarded as unacceptable or reprehensible, such as being the executor of an estate or an heir or legatee as a private person.

(3) The “trafficking dimension” at the time the Diplomatic Convention was concluded

122. None of the parties in this appeal, or apparently in Reyes, was able to point to any express discussion in the travaux préparatoires of the trafficking of domestic servants. But we are nevertheless satisfied that at the time the Diplomatic Convention was concluded there was no intention on the part of the contracting states that the phrase “commercial activity” could extend to a contract of employment where the worker was trafficked or otherwise exploited. On this point we note that the Supreme Court in Reyes was unanimous. Lord Wilson, who expressed his doubts about the answer proposed by Lord Sumption, accepted that when agreeing to the terms of the Diplomatic Convention in 1961, the parties would not have regarded a claim brought by Ms Reyes as relating to any commercial activity exercised by Mr Al-Malki. He said that he was persuaded that:

123. The doubts that the majority in the Supreme Court expressed in Reyes concerned whether the later developments in international law demonstrating the determination of many states to take steps to punish and eliminate human trafficking, particularly the adoption of the Palermo Protocol, could affect the interpretation of the exception so that it could now be said to encompass trafficked employment. We turn then to consider the case put by Mr Otty QC to this Court in the present proceedings as to the current meaning of the term and the conclusions arrived at by the majority.

(4) Has the meaning of “commercial activity” changed over time?

124. The case presented to the Supreme Court in Reyes and in this appeal as to the changing scope of the exception in the light of international law developments was a narrow one. As recorded by Lord Sumption in Reyes, Ms Reyes had confined her argument to the proposition that the international obligation to recognise a crime and tort of human trafficking affected the scope of the exception. It was not submitted before the Supreme Court in Reyes that the exception had extended to trafficked domestic workers when the Diplomatic Convention was concluded in 1961 or that the exception extended now to employment which did not fall within the definition of trafficking in the Palermo Protocol. Mr Otty QC's case before us at the hearing was similarly narrow. He declined to be drawn on whether a domestic worker who could not establish that she had been trafficked within the meaning of the Palermo Protocol would be able to rely on the exception, since, he said, he did not have to argue anything that wide. Indeed, one of the issues in dispute at the hearing was whether Ms Wong had sufficiently pleaded facts that amounted to trafficking within that definition. We agree with the courts below and with the majority that the appeal should proceed on the basis that the pleaded facts do allege trafficking within the meaning of the Palermo Protocol.

125. We would add that, in light of these pleaded and assumed facts concerned with trafficking, we do not consider that Ms Wong should be permitted to raise an alternative case at this late stage based on forced labour and/or domestic servitude. Ms Wong was invited by the Supreme Court to address this by written submissions subsequent to the hearing, and so we make no criticism of her attempt to do so. However, Ms Wong's pleaded case and arguments before the Employment Tribunal and Employment Appeal Tribunal were limited to human trafficking, as was the oral argument before us. In oral submissions before this court Mr Otty QC expressly accepted that Ms Wong's case rested on the international definition of trafficking being met. In our view, it would be inappropriate to allow Ms Wong, following the hearing before this court, to advance for the first time this alternative case. We do not have the benefit of the consideration of this case by the courts below and it would involve this court making effectively a first instance determination, from which, moreover, there is no possibility of appeal.

126. In addition, we disagree with Ms Wong that the allegations made in her ET1 claim form are sufficient to permit her claim nonetheless now to be characterised as relating to forced labour and/or domestic servitude.

127. Forced labour is defined in article 2(1) of the Forced Labour Convention, 1930, No 29 as “all work or service which is exacted from any person under the menace of any penalty and for which the said person has not offered himself voluntarily”. It requires it to be demonstrated both that there is a threat of a penalty should the labour not be performed and that the work is performed against the will of the person concerned (ie with an absence of consent or free choice) - see, for example, the decision of the European Court of Human Rights (“ECtHR”) in Van der Mussele v Belgium (1983) 6 EHRR 163, para 34.

128. Servitude is the obligation to perform certain services imposed by the use of coercion and is linked with the concept of slavery - see, for example, Siliadin v France (2006) 43 EHRR 16, para 124. It is a “particularly serious form of denial of liberty” and “corresponds to a special type of forced or compulsory labour or, in other words, ‘aggravated’ forced or compulsory labour” - see CN and V v France (Application No 67724/09), paras 89 and 91. As stated in that case at para 91, the distinguishing feature between servitude and forced labour is the victim of servitude's feeling that their condition is permanent and unlikely to change.

129. The ET1 and Ms Wong's Grounds of Complaint would not have been reasonably understood by Mr Basfar or his legal representatives as relating to forced labour or domestic servitude. They assert that she is a “victim of trafficking”. They do not allege that she is a victim of forced labour, that there was a threat of penalty or that the work was performed against her will. They do not allege that she is a victim of domestic servitude, or that there were any aggravating factors which would turn a situation of forced labour into domestic servitude, that Ms Wong felt her condition was permanent and unlikely to change, or that there were objective grounds for any such belief. In our view Ms Wong could not succeed in a claim based on either forced labour or domestic servitude on the basis of her claim as pleaded. This further persuades us that the claim should be limited to the assumed basis of human trafficking as pleaded in the appellant's ET1 form. We focus therefore on solely the human trafficking context.

130. We need first to address the question whether the words “commercial activity” are capable of changing their content at all. Ms Wong relied on Costa Rica v Nicaragua (2009) ICJ Rep 213, para 64. In that case the International Court of Justice considered the meaning of the phrase “for the purposes of commerce” in the treaty between the two states, granting the right of free navigation to Costa Rica only for such purposes. Costa Rica argued that the phrase included tourism although no tourism existed at the time the Treaty was concluded. The Court referred to the Vienna Convention on the Law of Treaties 1969: at para 64.

131. The Court went on to hold that where the parties have used generic terms in a treaty, the parties necessarily having been aware that the meaning of the terms was likely to evolve over time, and where the treaty has been entered into for a very long period or is “of continuing duration”, the parties must be presumed, as a general rule, to have intended those terms to have an evolving meaning.

132. Lord Sumption said at para 43 in Reyes that there is nothing in the wording of the Diplomatic Convention from which one could discern that the concept of “professional or commercial activity” was ambulatory:

133. On this point we respectfully doubt that conclusion to this extent: the phrase can have an ambulatory meaning in a more limited sense. Businesses that did not exist in 1961 such as mining cryptocurrencies, designing computer games or trading in financial derivatives might well, in our view, count as exercising a commercial activity even though they were not activities that existed when the Diplomatic Convention was adopted. That is the sense in which an ambulatory meaning was given to the term “for the purposes of commerce” in the Costa Rica case so that it included the transport of tourists on boats along the river even though no such tourism had taken place when the Treaty had been signed in 1858. It is not difficult to accept that the drafters of the Diplomatic Convention would intend that the words could expand in their meaning over future years for that purpose.

134. Here, however, we are dealing with a different kind of ambulatory meaning. Human trafficking and the exploitation of vulnerable workers did not start after 1961; it has always existed on varying scales. The question is whether the adoption of measures by the international community exhorting countries to punish perpetrators and compensate victims has changed the content of the phrase “commercial activity” so that it now does encompass trafficking. It is not possible simply to make the leap from the developments in the law as to human trafficking to a conclusion that those developments have affected the meaning of words in an earlier international instrument. In addressing that question, one must, as Lord Sumption said at para 42 of Reyes approach the matter using legitimate techniques of interpretation, subject to principled limits. That much is also clearly established by the two cases in which similar submissions were made: Barnet London Borough Council v Attorney General and the Secretary of State for Foreign, Commonwealth and Development Affairs [2021] EWHC 1253 (Fam); [2021] Fam 404 (“Barnet”) and Jones v Ministry of the Interior of the Kingdom of Saudi ArabiaJones”).

135. In Barnet the argument before the Divisional Court (Sir Andrew Macfarlane P and Sir Duncan Ouseley (sitting as a High Court judge)) concerned the effect, if any, of the adoption of the UN Convention on the Rights of the Child (1989) (Cm 1976) on the scope of diplomatic immunity. More precisely, the issue before the court was whether the positive obligations under article 3 ECHR, required a new exception which would apply where the diplomat was accused of abusing his children in breach of their article 3 rights. The Court rejected a submission that the UNCRC and the ECHR could have superseded the provisions of the Diplomatic Convention (which they referred to as the “VCDR”):

136. This was a similar exercise to that which the House of Lords conducted in Jones. In that case the immunity invoked was state immunity rather than diplomatic immunity but the approach is still instructive. The issue for the House was to consider the balance currently struck in international law “between the condemnation of torture as an international crime against humanity and the principle that states must treat each other as equals not to be subjected to each other's jurisdiction”: para 1. Lord Bingham of Cornhill described the new and important consensus of the nations of the world as to the “extreme revulsion” for the practice and fruits of torture, as expressed in the UN Convention against Torture and other Cruel, Inhuman or Degrading Treatment or Punishment 1984 (1990) (Cm 1775): para 15. The Torture Convention had come into force in June 1987 and both the UK and Saudi Arabia (with the overwhelming majority of other states) were parties. It was also common ground that the proscription of torture in the Torture Convention had, in international law, the special authority of ius cogens. The claimants’ key submission was that the proscription of torture by international law, having the authority it did, precluded the grant of immunity to states or individuals sued for committing acts of torture. Such acts could not be governmental acts or exercises of state authority entitled to the protection of state immunity ratione materiae.

137. Lord Bingham rejected that submission. He held that neither the prohibition on torture nor that on crimes against humanity automatically overrode all other rules of international law. He said that it may very well be that the claimants’ contention would come to represent the law of nations but it could not be said to do so now. Lord Hoffmann also rejected the submission that the fact that the prohibition on torture was ius cogens meant that it overrode immunity:

He went on: (para 46)

138. Lord Hoffmann said further, at para 63, that international law is based on the consent of nations so that it is not for a national court to “develop” international law “by unilaterally adopting a version of that law which, however desirable, forward- looking and reflective of values it may be, is simply not accepted by other states”. He concluded that there was nothing in either the Torture Convention or the United Nations Convention on Jurisdictional Immunities of States and Their Property (2004) to indicate that a new exception was so recognised. He considered judicial decisions of the International Criminal Court and the ECtHR and then national courts. Lord Rodger of Earlsferry and Lord Walker of Gestingthorpe and Lord Carswell agreed with both Lord Bingham and Lord Hoffmann.

139. The majority's judgment in the present appeal does not state that it is overruling the decision of the Divisional Court in Barnet but it is difficult to see how that decision can stand, assuming one regards child abuse falling within article 3 ECHR as being serious misconduct which is widely condemned by the international community. It is true that the present appeal is different from Barnet and Jones in that those cases were considering the insertion of a wholly new exception rather than a new and wider interpretation of an existing exception. But the same principles must apply since the principle that the words must mean the same for all signatories applies just as much to the proposed extension of meaning of an existing exception as it does to the creation of a new exception. Further, the potential effect on diplomatic relations - the risks of real harm to our diplomats abroad arising from disturbing the Diplomatic Convention to which the Divisional Court referred in Barnet - is the same in both situations.

140. To adapt what Lord Hoffmann observed in para 46 of Jones set out above to the facts of the present case, whether an exception to diplomatic immunity has come to be recognised by international law in the extension of the phrase “commercial activity” to the employment of a trafficked domestic worker must be ascertained from treaties, judicial decisions and writings of reputed publicists.

141. So far as treaties are concerned, we consider that the same answer must be given as regards the effect of the Palermo Protocol on the Diplomatic Convention as was given by the House of Lords in Jones as regards the effect of the Torture Convention on the scope of state immunity. Mr Otty QC is not able to point to anything in the Palermo Protocol that deals with the scope of diplomatic immunity. It cannot be the case that a treaty obligation to make certain conduct a serious criminal offence is itself enough to require contracting states to lift immunity for that conduct: the immunity of diplomats from criminal prosecution is complete and is not challenged in these proceedings.

142. As to state practice, the jurisprudence from the courts of other parties to the Diplomatic Convention point very firmly towards the continuing state practice being that the employment of trafficked domestic workers does not amount to commercial activity for the purposes of article 31(1)(c).

143. We were taken to a series of cases in which the courts in the US have firmly rejected cases on similar facts to those of Ms Wong. The primary authority to which these cases refer is an authority from the United States Tabion v Mufti (1996) 73 F 3d 535 (“Tabion”). We agree with Lord Sumption's comment in Reyes at para 22 that decisions of the federal courts of the United States are a valuable source of law in this area, “because of the long-standing engagement of the US courts with international law and the existence of a highly developed body of domestic foreign relations law belonging to the same tradition as our own”. In Tabion the claimant worked as a domestic servant in the home of a Jordanian diplomat stationed in Washington. She brought an action alleging breach of United States labour laws. The US Court of Appeals Fourth Circuit (on appeal from the District Court) held that the term “commercial activity” did not extend to include occasional service contracts but related only to trade or business activities engaged in for personal profit. The Court concluded:

144. Although Ms Tabion's claims included claims for low pay, long hours and false imprisonment, the case did not raise squarely the question whether the conditions under which she worked affected whether her employment amounted to “commercial activity”. This was dealt with more directly in later cases. In Sabbithi v Al Saleh (2009) 605 F Supp 2d 122, the plaintiffs were domestic workers from India bringing an action against their former employers who were Kuwaiti diplomats. They brought proceedings under the Trafficking Victims Protection Act of 2000 (“TVPA”) and the Fair Labor Standards Act. The plaintiffs had been employed by the defendants in their home in Kuwait prior to moving to the US. It was alleged that in Kuwait they had worked long hours, seven days a week for small payment. On coming to the US, they signed employment contracts promising to pay them considerably more and to comply with US labour laws. These contracts were presented to the US Embassy in Kuwait for the purpose of obtaining visas to authorise the plaintiffs to work in the defendants’ home in the US. The plaintiffs claimed that once in the US, the defendants did not comply with the terms of the contracts but maintained their exploitative treatment depriving them of their passports, threatening them with physical harm and physically abusing one of them. When they escaped and filed suit, Kuwait declined to waive immunity.

145. The arguments put forward by the plaintiffs in Sabbithi relevant to the present appeal were (1) the defendants’ alleged trafficking of the plaintiffs fell within the “commercial activities” exception to immunity under the Diplomatic Convention; (2) diplomatic immunity could not bar the plaintiffs’ claims because the defendants’ actions were so egregious they violated ius cogens norms prohibiting slavery and slavery-like practices; and (3) the plaintiffs’ claims under the TVPA prevailed over the defendants’ conflicting claims of diplomatic immunity according to the “subsequent-in- time” rule. The District Court rejected those arguments. The court was not persuaded that the defendants’ alleged conduct constituted human trafficking and held that no ius cogens norm was at issue. But it went on to say that, in any event, there was no evidence that the international community has come to recognise a ius cogens exception to diplomatic immunity. The Court then went on to come to a different conclusion from the Supreme Court in Reyes, holding that the immunity extended after the defendants returned to Kuwait because it was part of the exercise of their diplomatic functions.

146. This has been the interpretation of article 31(1)(c) approved by the US courts in more recent cases. In 2011, the claimant in Montuya v Chedid (2011) 779 F Supp 2d 60 alleged that she was brought to the US in August 2007 to work in the home of the Lebanese ambassador as their domestic servant. She was forced to work long hours for little pay and was verbally abused and insulted. She claimed she was not allowed to leave the defendants’ home and was illegally confined there. The court referred to the Sabbithi case and found the reasoning persuasive. The court said in closing:

147. Finally as regards the US jurisprudence, the question of trafficking was raised squarely in Fun v Pulgar (2014) 993 F Supp 2d 470 (decision of the US District Court). There the plaintiff was offered work as a live-in domestic worker for the family of a Peruvian diplomat working at the Permanent Mission of Peru to the United Nations. She was supplied with an employment contract setting out favourable terms but once she arrived in the United States, the defendants confiscated her passport and put her immediately to work. She alleged that the defendants’ actions created a human trafficking and alien harbouring enterprise in order to take advantage of her service as an underpaid domestic servant. The plaintiff claimed damages and injunctive relief for being trafficked into the United States by the defendants and forced to work against her will as their domestic servant for over six months. The District Court still held that the claim did not relate to commercial activity within article 31(1)(c), applying Tabion. The court did not regard the conditions under which she worked as capable of converting her employment into a commercial activity.

148. The only case on which Mr Otty QC could rely is the Portuguese case of Fonseca v Larren 30 January 1991 reported in “State Practice regarding State Immunities” edited by the Council of Europe. This was an appeal before the Supremo Tribunal de Justiça. The report provided to us can be set out in its totality:

149. We have no reason to disagree with Lord Sumption's analysis of this case at para 33 of Reyes where, apparently having access to a fuller report of the decision, he explained the result as arising from a principle of statutory construction sanctioned by the Portuguese Civil Code which would not apply to a treaty in England. Curiously, the page containing this report in the Court's appeal bundle contains a report of a later decision on 4 May 1994 in.the District Court of Lisbon in Ramos v US Government. In that case it appears that the Lisbon Court held that “Portuguese courts are internationally incompetent to judge labour contracts entered into with the US Diplomatic Mission in Portugal, since this State has not waived its immunity from jurisdiction.”

150. We accept that the Supreme Court in Reyes has already created a difference of interpretation by holding that the employment of domestic workers is not part of the diplomat's official functions so that immunity for employment related claims does not continue once the diplomat leaves office. The contrary conclusion has been reached by the US Courts. Whether or not the majority judgment means that the US cases were wrongly decided is not the main point here. The relevance of the US cases for present purposes is that they are very far from showing that there is state practice to support a contention that the parties to the Diplomatic Convention have recognised that the development of international law about trafficking and slavery has affected the meaning of the term “commercial activity” in the treaty to which they are all party.

151. As to writings of reputed international lawyers, we were shown nothing to suggest that legal writings recognise the extension of the term “commercial activity”. On the contrary, Professor Denza refers without criticism to the decision of the US court in Tabion and to the application of that principle by the Court of Appeal in Reyes: see pp 251–252 of her Commentary. She refers also in her Introduction to the resilience of diplomatic immunity in the face of evolving human rights norms:

152. We therefore agree with Lord Sumption's conclusion in Reyes that there is nothing either in the Palermo Protocol or in the other international treaties, or in state practice or in academic writings to support the proposition that the meaning of “commercial activity” has changed since 1961 so that it now encompasses trafficked employment of the kind Ms Wong alleges.

153. For completeness, we add that even if Ms Wong's claim can be characterised and advanced as relating to forced labour and/or domestic servitude (contrary to our conclusions at paras 125-129), our view is that this makes no difference to the question of whether Mr Basfar was engaged in “commercial activity”. We consider that Ms Wong is wrong to suggest that forced labour and domestic servitude amounts to a “commercial activity” for the purposes of article 31(1)(c) because a perpetrator makes financial savings by not paying the required rate for that labour. For the reasons we have given above, in our view the correct approach is to consider whether the activity in which the forced labour or domestic servitude is used can be considered a “commercial activity”. The forced labour or domestic servitude is not itself a “commercial activity”. In the present case, Ms Wong's labour was clearly carried out in a domestic setting rather than being put towards any kind of profit-making activity by Mr Basfar. The fact that, on the assumed facts, Mr Basfar's treatment of Ms Wong was of an appalling nature does not mean that he was engaged in a “commercial activity”.

154. As Lord Sumption recognised in the context of human trafficking in Reyes at para 45, there is nothing inherent in forced labour or domestic servitude that they be carried out in the exercise of a commercial activity. The characterisation of working conditions as forced labour or domestic servitude does not depend on whether a “commercial activity” is carried on by the perpetrator, nor on whether the perpetrator intends to make savings or a profit, but rather on the perpetrator's treatment of the victim and whether it involves the denial of the personal autonomy and dignity of the victim.

(5) Problems arising from the majority's decision

155. Ms Wong's appeal before the Court has been conducted on the basis that the facts she asserts in her pleaded case before the Employment Tribunal are true. The majority judgment has set out those facts and, if true, they disclose shocking and shameful mistreatment. The same was true of the facts assumed in Barnet that the diplomatic agent's mistreatment of his children had been so severe as to amount to a breach of their article 3 Convention rights and in Jones where the claimants pleaded particulars of severe, systematic and injurious torture. Although this Court does not have to examine whether Ms Wong's allegations are true, that does not absolve us from the need to consider the worrying difficulties that one can foresee arising from a decision that trafficked or other exploitative employment is a “commercial activity” for the purposes of the exception. We see these difficulties as arising on a number of fronts:

1. () The difficulty in defining what amounts to trafficking and the breadth of that definition;

2. () The intrusive nature of the enquiry that the tribunal would need to carry out to determine whether immunity applied or not;

3. () The scope of the exception if it is extended beyond trafficking to cover other forms of slavery or exploitative employment;

4. () The risks to the UK's diplomats abroad from the expansion of the exception.