However London is a global cultural and trade hub entirely due to it's finance industry. Take that away and what does London or Britain have economically? Every single London resident would suffer from that from lower wages, fewer employment prospects and higher taxes. Property would be less valuable and so rents might fall, but so would earnings to pay for it with.

I fully expect a 'we should be making cars (or whatever) instead of running banks' type argument, but why is that a choice? Anything else we could do to make up for losing Finance we could do anyway. We had a 3 term Labour government. They were in power for 13 years. If anyone was going to dial back the clock and 'save' Britain by turning it into a low-wage, low value jobs-for-the-boys economy they had the chance. Killing finance first then wondering what to do instead is kind of the wrong way to go about something like that.