On 23 June 2016, the people of the United Kingdom voted to leave the European Union. On 31 January 2019, the UK formally left. The question as to whether the UK would “really” leave was thus definitively answered. Although, under the terms of the Withdrawal Agreement, a transitional period running until 31 December 2020 is currently under way (and may be extended, once only, for one or two years), the UK is now, in EU terms, a third country. Although it was never imagined that it would be used by the UK, Treaty on European Union (TEU) Article 50 has served its purpose and is no longer relevant. The only way back into the EU would be through the provisions of TEU Article 49, which would see the UK applying again for membership as a third country. All of the UK's hard-won accumulated exceptionalism has gone for all time: no more rebate, no opt-out of the single currency and the Schengen agreement on the dismantlement of frontiers, no opt-in to justice and home affairs provisions, no February 2016 New Settlement. All gone.

Thus, one question has been definitively answered, but another remains open. Just what sort of future relationship will the UK enjoy with the EU? This is a question of obvious significance for both sides and yet, strangely if understandably, it was hardly debated, let alone answered, in the run-up to the 23 June 2016 Brexit referendum. Moreover, it is a question that, ultimately, can only be answered by both sides together. Equally understandably, once the referendum result was known, debates began, both in the UK and in the EU, about what the answer to the question might be, bookended by debates about what it could be and what it should be. Almost immediately, alternative models were suggested, and these tended to be associated with particular countries; for example, “Norway”, “Canada +”, “Switzerland”, “Singapore on the Thames”, “Ukraine” and so on. But what exactly do such models entail, and how have they evolved? What are their perceived advantages and disadvantages, especially for the countries concerned?