The United Kingdom’s decision to leave the European Union will reshape the EU and, in particular, the EU’s institutions. The European Parliament will lose 73 British members. The Commission will have one Commissioner fewer and will have to deal with the more than 1,000 British nationals it employs. The Council of the EU will see a change in its balance of votes – and consequently in its voting patterns. The Economic and Social Committee and the Committee of the Regions will lose their British members, and the future of thousands of Britons working in the wider EU policy-making community has become uncertain.

Britain’s decision is near-universally seen as a negative one for the EU, although opinion is also united in thinking it will likely be much worse for the UK. There was little the EU institutions could do to avoid this scenario, however: the UK was the main actor and the room of manoeuvre for EU institutions was limited. How, then, did the European Commission, the European Parliament and the Council act and react during this process triggered by one of the EU’s member states?

From the moment the then UK prime minister, David Cameron, informed his counterparts of his intention to hold an in/out referendum and to renegotiate the UK–EU relationship up until the day he lost the referendum, the EU institutions played, at best, the role of a supporting actor. But, once the fate of the UK’s membership had been sealed by the vote, the EU institutions took centre stage in order to strengthen the unity of the 27 remaining member states. The UK progressively and rather quickly became de facto a “third country” for the EU. This was aided by the sense of distance that had been created during the referendum campaign, which the EU institutions felt was fought on misinformation and with only a half-hearted endorsement of EU membership by many key British political actors.

This chapter retraces the process that transformed a complicated but mutually beneficial relationship into a lose–lose situation, characterized by a rapidly growing estrangement between both sides.