I'm sure everyone know about this, but there is the problem of hysteresis when it comes to businesses moving elsewhere. There is a cost of moving from A to B, but if you do so, and subsequently then consider moving back, the costs are similar: you don't get it back. So, informally, if we lost a significant part of the finance industries as Brexit approached, and then decided to back out and to stay in the EU, those who had moved would, in the main, stay where they are; we would have to offer a much bigger incentive to persuade them to come back to the UK once that had achieved the transitions to, say, Paris or Frankfurt.