[marksweston]

Historically it seems that the highest paid developers in London have been contractors, who can charge £600 ($780) / day for fairly non-niche skills in web-development.

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.