This also means that whatever the bill ends up being, it is a sunk cost. We’d definitely have to pay if we stayed, we’re going to have to pay – preferably a figure at the lower end of the range – if we leave, thus the bill has no effect whatsoever on the decision to stay or go. That’s what we mean by sunk cost.
To put this another way, to remain would be to sign up to a never ending series of those €100 billion payments, to leave is to draw that line in the sand beyond which we can indeed spend the cash on the NHS if we so wish. Or even not tax ourselves and leave the money fructifying in our pockets.
There simply isn’t a Brexit divorce bill at all, there’s only a clarification of how much continued membership would cost us.