Britain is a hub of high-tech manufacturing. We have one of biggest aerospace industries in the world and Roll Royce is the world’s second largest manufacturer of aircraft engines in the world, second only to GE. The City of London has been one of the world’s leading financial centres for centuries, much of it centred around insurance and brokerage. The real dodgy money goes into Switzerland and the Cayman Islands, not London. London is no worse than NYC and I doubt NYC is going to go away as a financial centre either.
How long before RR is moving production to China or India? You won’t ride on this mule forever anyway.
As for banks I said earlier. Services. A parking spot for criminal money. A little more rounds of sanction games and it would move elsewhere.