David looking for the trees you are missing the woods altogether.
You must strengthen the Commonwealth Trade Organisation on same lines as EU first and then only you will have an upper hand in negotiating with the EU.
Ask India,Canada,Australia,South Africa to vigerously start the Commonwealth Trade Common Market and you will never look back.The Commonwealth Common Market should be heavily inclusive on all issued including the Banking which the British Banks can organise very well along with other countries.
Regards and God Bless
Viren Naik