As we've pointed out before there is no such thing as the Brexit divorce bill. This is not to take sides in the current argument - although some of us are known to be highly partial, even prejudiced, upon the subject - it is to point out a basic economic, even accounting, point.

Sunk costs are sunk costs and they do not and therefore should not influence our decisions. This is akin to probability. Before we throw a normal die there is a 1 in 6 chance of any one number. After we have done so then the result has a probability of 1. It has happened. So it is with sunk costs.

Whatever the number is, whether it's €100 billion or whatever change we deign to toss into into the EU's will politic for food begging cup, this is still the wrong answer:

But those remainers who feel no obligation to defend this government have every right to be as appalled by this £50bn bill as Farage and co. They – we – can see that it’s necessary for a club member to honour their debts as they leave after 44 years of membership. But, boy, what an unforgivable waste of money.

For let’s remind ourselves of the basic truth here. We’ll be paying this money for the privilege of not being in the European club.

This is not true in the slightest. Recall what the EU's position is. You have agreed to pay this as a part of your membership. If you leave you should still pay the amount you agreed to pay.

OK. Or maybe not OK to taste. But quite obviously, if we pay whether we go or stay then it's not a cost of either going or staying, is it? It's a sunk cost, a result of decisions taken in the past and decisions made now won't alter it in the slightest.

It is true that leaving means we're not signing up to a continual stream of such future payments. But meeting our current contractual obligations is a sunk cost, one that we'll have to pay whatever. It's thus not a useful fact to include in our decision process, just because the decision either way makes no difference to us.

Yes, really, sunk costs are sunk costs.