Ideally, anyone could wear whatever they want whenever they want. In practice, it doesn't seem to work out this way, even at the tshirts and jeans companies.
What kind of company did you work for where this happened?
Banking salaries have been static for 10+ years. Bank internship salaries are designed to allure and impress but 5+ years in and the salary does not change.
On another note there are some startups who can pay very very well in London but they do not advertise these salaries.
Are tech companies open to hiring from different industries, like the ones listed above?
A year or so ago I received an offer from a well known quant hedge fund, I spoke to a google recruiter to see if they could match, to my surprise right there on the phone he told me they never get beat out and that they would beat the offer by 50k.
The hours are much better in tech, you get treated better, and at Facebook/Google/Amazon/other big tech firm you have less variance in pay.
You should seriously question your compensation if a recruiter is willing to top you up 50k without a second thought. Chances are you are severely underpaid.
They want you for as cheap as they can get you but if someone else is willing to pay more then almost always they can afford it.
I quit last year to look after my kids and do my own thing, although the decision was driven more by boredom than any desire for more pay.