IR35 may change the incentives for employers enough that that kind of money is more likely to be paid in salary form. We're now seeing senior developer salaries being advertised as high as £90k - £100k ($130k). Again, for in demand but non-niche skills (Ruby, React, full-stack JS etc).
I'm sure London won't be seeing SF or NYC level salaries, but you can definitely live comfortably in London on a software engineer's salary.
Overall your total comp can get well beyond 150-160K GBP these days, that's including the 15-20% cash bonus, and the circa 20% pension large companies award today + other benefits.
It's certainly harder than in, say, SF, but by no means impossible. Google and Facebook between them have thousands of engineers in London and are growing fast. They're not paying as much as the US, but are by no means stingy. £100k ($130k) is not unrealistic.
If you want some anecdotal data, I transferred from the Bay Area to London and my base salary decreased about 25%. But then again, a nice one-bed apartment in London can easily be easily found for $2k...try finding that in SF.
Yet I work in a a medium-to-low COL area of the US and make more than that. My area is in the high 80's while NYC is 162 and SF is 206.
It's hard to argue in favor of being a SWE in London if being a SWE in the US is a possibility in any locale.
There just is not that kind of money in circulation for SWE.
I even doubt one can get $130k in London.SWEs in London are not competing with other SWEs. They are competing with bankers and similar.