I have made the case for why progressives and federalists outside the UK ought to advocate Brexit (for the sake of the political integration of the rest of the EU), and I have also tried to examine in a bit more depth how the outcome of the vote might have implications for Cameron’s successor as Prime Minister (in short: if the UK remains, it helps Boris – although he’s stated he’s pro-Brexit).

In this blog entry I am going to try to work out how the EU ought to play it if the UK remains in the EU after the vote on 23rd June, but ends up with a Prime Minister who had advocated Brexit in the referendum campaign.

As a point of departure it’s worth noting that other EU Member States are not unaware of the difficult precedent the UK might be setting with its referendum – at the insistence of France and Belgium (according to the FT), a self destruct clause was inserted in the deal for the UK, meaning if the UK exits other states cannot try to extract the same sort of concessions – UK out means the deal is null and void.

This is also important as it essentially ended the debate that the UK could vote to leave, extract more concessions, and then hold another referendum to stay on even more special terms – this was a procedure that Boris had advocated, before changing his mind.

Among politicians across the rest of the EU I detect a kind of willingness to keep Britain in the EU expressed through gritted teeth – we’ve done what we can for the UK this time, but that’s it. That means that if a pro-Brexit Prime Minister from the UK comes to the EU institutions any time within the next few years demanding a special deal for the UK once more, or threatening a further referendum, the reaction is not going to be as accommodating as it was towards Cameron. You might have the words the Belgian PM apparently once said to Cameron – “If you want to go, just go. We will not let you ruin Europe by staying.” – being more openly repeated.

Some commentators in the UK have expressed the fear that the current referendum will only be the start of instability of UK-EU relations and that, like in Scotland, this first vote is the start of a neverendum. The response to this from the rest of the EU has to be resolute if Britain remains – the deal negotiated with Cameron was done in good faith, Britain voted to stay, and hence the British cannot keep threatening further referendums. Any future pro-Brexit Prime Minister would do well to understand this – and that the leverage the British have would decrease, not increase.

But what then about the UK’s behaviour in the EU institutions?

Here there are two levels to consider – everyday policymaking, and decisions about the future institutional setup of the EU.

On the everyday policymaking level, Britain has already started to exclude itself – as Simon Hix’s Council data shows, the number of times that the UK was outvoted when majority voting applied has shot up from 2.6% of cases in 2004-09 to 12.3% in 2009-15. Lobbyists have started to build the UK’s lack of influence into their strategies (see this from the FT – paywalled) and work with others instead. In the European Parliament the UK punches well below its weight as so few British MEPs sit in the major EPP and S&D groups. All of this makes one wonder why the European Commission paid so much attention to the UK in its Better Regulation Agenda – perhaps we might learn this after the referendum and the do less mantra of the EU might be somewhat relaxed. But, as I see it, the UK is currently marginalising itself in the everyday work of the EU, and that is not about to cease.

When it comes to the further integration of the EU in the future, the picture may also not be too bad. Unlike Tony Blair – who promised to put the UK at the heart of Europe but then failed to do it in practice – Tories currently do not even pay lip service to the idea that the UK is central. Osborne’s views on the necessity of Eurozone integration are well known; he just sees no role for the UK in that further integration, but would not stop the rest. In 2011 the other Member States of the EU managed to sort out the Fiscal Compact anyway, building a way around Cameron’s ‘veto’. The European Public Prosecutor can be implemented without the UK taking part.

All of this is the sort of approach suggsted by Andrew Duff with his Protocol of Frankfurt idea – essentially leave the EU where it is, and advance other causes and policy areas by going beyond what the EU currently does in the areas where this is judged necessary, and doing this with sub-groups of Member States.

So that, I think, is how the EU could handle a reticent United Kingdom – if the UK chooses to Remain on 23rd June, but then ends up with a pro-Brexit Prime Minister shortly afterwards. Brussels would have to endure some pretty nasty rhetoric from the UK no doubt, but on the substance, Britain’s self imposed part marginalisation might not be all bad.