Directly employed is appx. 1.2 million. Total working population is roughly 32.5 million.
Almost 4% of the total. So you did not mean that literally - what did you mean?
Second, although the City stats overstate their importance to the UK economy, the slice of the 'earnings' they may contribute is arguably 10 odd %.
You are right that the UK has lost its manufacturing base, a conscious neolib ploy by Thatcher, disenfranchising the UK unionised working people ... and?
But seriously, imo the financial grip of the City shan't be catastrophically loosened by the competing gangstas. No worries, they are extremely agile: