Some amount of guff written here about banks moving. The same guff that was written when Britain declined to join the euro. I believe Frankfurt was to eclipse London utterly...
European banking (and indeed much of the world outside the US) is dominated by LMA standard documentation and English law, banks have vast capital expenditures in moving, and much of their business doesn't require an EU presence per se, especially as they can then chuck MiFID, AIFMD etc.
This is obviously horribly off-topic, but in the interest of balance: I've been told on an off the record basis by numerous institutional investors that the vast flow of EU capital into the UK is very much at risk if Britain leaves the EU. Make of it what you will, but if there's little European investment coming into the UK it makes absolute sense that firms will move significant chunks of their operations to territories that will see such activity - particularly non-EU businesses using London as a base for their European operations. It may or may not be true for the rest of the economy but the financial sector is very much at risk.