That's base salary, and there will be pension contributions, benefits, maybe worthless options, etc, but not a stock package that doubles the total comp.
High finance and FAANGs with London offices pay much more - more base salary, and chunky stock or bonus packages. Not all of finance pays well - plenty of high-street banks pay their developers poorly (and it shows). I work in a successful trading firm and earn comparably to an L5 at Google, according to levels.fyi.
Day rates for contractors seem to vary a lot, but 400 - 600 a day, maybe? The contracting scene is still adapting to recent tax law changes, though.
This is assuming we're talking about programmers. Median salary across the whole of London is ~40k. Tons of people earning 20k working in a shop etc.
On the permanent positions, that sounds like a seniority thing. The people I know aren't staff or principal. I know someone who's sort of head of engineering at a small but healthy startup, and I think he's on 120k or something.
As to day rates I think it's rather about companies willing to pay a bit more to get better contractors rather than any specific stack.