I'm a mid level engineer earning £45k in Bristol, not including additional benefits and perks. To get that I moved from a small company to a very big software employer in the UK. I've found that UK salaries have a massive range but it's pretty much the big companies paying the top end ones, and then all the rest paying the lower ones.

I have many friends with the same years of experience as myself, and similar tech stacks. They're working for smaller organisations across the south of England and on roughly £28-30k with few/no perks past the standard UK pension payments.

I think a lot of people are underpaid in the UK (including the parent poster), in particular those at smaller companies and smaller consulting agencies. However I imagine it's less of an issue in London.