I'll just say on the subject of the banks movements; That most of the banks that people cite as fleeing London are not actually leaving London at all. It's just a sensible design, now, to have a base in both London and Europe, separately established. This isn't panicked changes occurring, it's carefully planned and thought out redistribution.
There's no sensible reason not to have a foothold in Europe specifically, while also maintaining existing positions in New York and London. Common sense would tell you that a change in world borders would require a careful distribution of offices and the required level of employees, to maintain status quo.