One always had to wonder why Deutsche Bank needs 9000 people in London, or HSBC needs 43000 in the UK. Was that not always padded by quite a bit or over staffing? Given the arrival of Fintech and the plummeting cost of communicating with low-cost centres there was always the prospect of job diversion, especially in support roles. Globalization also means that other centres such as Dubai, Singapore, Shanghai etc would grow in stature and staff would be relocated closer to customers and markets.
In the opposite direction there are forces that might in the long run strengthen the role as hub and nerve centre coordinating and directing the regional centres. Higher Value-added roles might well be concentrated in the UK - if politics and regulation are creating a business-friendly environment.