Suppose membership of the EU is like being a member of a club. When you leave a club you aren’t liable to keep paying the club money to finance all the things the club has committed to paying for the foreseeable future, like rent, salaries, pensions, and so on. That’s up to the club, and it’s also up to the club to get members in so that it has the money to pay for those things. So if membership of the EU is like membership of a club, then we don’t have any obligations to keep paying in money once we leave in order to pay for the EU’s future obligations, even when those things include paying the pensions of British people who worked for the EU. (Nor do we have any claim on the assets of the club.)
But maybe the EU should be conceived of as more like a partnership. Not that the people in charge of the EU act like it’s a partnership, they act like they’re in charge, and the member states should do what they’re told. But maybe, despite that, it is more like a partnership. But what happens when you leave a partnership, and the existing partners carry on the organisation? This is a complicated and tricky area even in normal business circumstances (and there are differences in types of partnerships, eg. the rules for a limited liability partnership are different those for a non-liability partnership). And it’s even trickier in this case.
A departing partner, especially one who has put in most of the money, or most of the work, may feel entitled to a share of the assets of the partnership. That person would not normally be expected to keep paying in money to finance the partnership’s financial commitments once they’ve left, and the others are carrying on. If the departing partner does agree to keep paying in for a while then it would be reasonable for them to claim a share of the assets of the partnership. It may be reasonable for them to claim a share even if they don’t keep paying in. Otherwise they walk away from something that they’ve put a lot of time and/or money into, which has made it a success, and they get nothing.
The UK has poured an enormous amount of money into the EU, and has helped turn it into a powerful institution. Yet we’re supposed to walk away with nothing for us, but £40 more billion for them? The EU has fancy buildings, fancy cars, fancy wine cellars, which they never would have had without our large contributions. Yet we get no share of those, or suitable compensation?
You might say that membership of the EU should not be conceived of as like a partnership either. You are probably right (after all, mainly what the EU does is to piss away its members’ contributions), but then what is it to be a member of the EU? How should we conceive of it? This is something that never gets discussed. Probably because the EU apparatchiks never even dreamed that anyone would want to leave, or be allowed to leave. But the nature of a country’s membership matters when it wants to depart. This trips up rock bands all the time. They never think about the nature of the partnership at the start, and when the group breaks up, they end up in the courts for years.
Update: The recent Brexit ‘agreement’ provides little detail on this, and little detail on what exactly is going to happen with our continued contributions. How much of the £39 billion is money we will owe anyway for the period up to March 2019 is not stated, although if we pay about £12-14 billion annually (after the rebate), as many sources say, then we’re only talking about £15-18 billion for that period. (But are there hidden payments that we normally make which aren’t declared as part of our official annual contribution?)
There will be some money paid back to the UK: it “will receive a share of any financial benefits that would have fallen to it had it remained a Member State.” But I take that to mean that we’ll still get the usual things we get, eg. grants to academics, while we’re continuing to pay in, rather than any share of the EU’s assets.
I also note that the agreement itself features the exact words (near the start), “Under the caveat that nothing is agreed until everything is agreed”. This wasn’t just some spin put on the agreement by David Davis. So why the fury on the part of the EU when this was brought up? Why do we need to put into UK law an agreement which itself contains the caveat that this interim agreement is not final until everything else is agreed?