up until the 70s, the average wage was higher in Birmingham than London. it was a conscious decision to pump up London and the south-east at the expense of the rest of the country, look up where the banking centres of the country actually were, 2 of the big 4 were Birmingham based..No, it wouldn't, you can't just replace financial services like that. No one is stopping anyone from opening up offices in Manchester, Birmingham etc.. it would be far cheaper to both rent the space and employ people for the start in reality financial service orgs tend to just stick IT and back office stuff in second-tier cities, the talent is in London. Likewise, the EU was hoping for a far bigger slice of the pie split across Frankfurt, Paris, Amsterdam etc..
You have it the wrong way around the talent isn't in London forcing companies to be there, the companies were encouraged to move their forcing the talent to move.