[user5994461]

The answer to how many places are big tech or finance is a truckload.

There are 10 000 employees in every building in canary wharf (the financial center with tens of banks). There are a similar amount of employees in the new buildings of Google, Apple and co. Plus multiple large companies but not necessarily as great. That's tens of thousands of roles to fill.

[toyg]

Those buildings are hardly full of developers. Most of them are accountants and boatfuls of bullshit jobs. I know because I work among them.

Look at Canary Wharf at lunchtime and tell me with a straight face that those are developers.

[user5994461]

Of course no building is full of a single thing. The one I worked in had full floors full of developers, that adds up to quite a decent amount.

Ironically, accountants and finance folks eat at their desks, so if you see people outside at lunch time, they might very well be technology folks. They'd be wearing shirts though, easily confused with business people.