People have to realise finance is global and powerful.EU institutions, business and citizens will have less access to financial markets, finance and legal experts in London. just as its a disadvantage for general UK business to have restricted access to larger EU market, it would be a disadvantage to restrict access to the larger UK finance market. Institutions here are allowed to freely trade in instruments there, but not vice versa, so an office in Londone can trade markets in both jurisdictions, a office based in Paris cant - which is more restricted?
A way will be found for an EU-UK finance deal.