My ancestors were prescient.
No money exchanged, no complicated trade deals, no "moving banks" around the EU (of which I'm involved in moving one to Luxembourg right now because of Brexit) just a simple "If you're here in Great Britain, carry on as normal" and the same rules for international banks located in Britain as British banks.
If the EU didn't like those terms, tough sh*t.
What is wrong with the country that bore the United States of America?