Top earning UK dev jobs are usually 200k upwards, already. Those numbers don't account for finance and similar industries, which they hire directly and don't use Hired services.
How common is this? Even breaking £150k seems really challenging - FAANGs aren't hiring in London right now, finance seems to require previous finance experience and/or prestigious education even for experienced candidates (I don't know if they really require it or just like to put it in their job ads); and even companies that pay less (£90-120k) aren't giving me the time of day.
I'm making more than that in London. I know similarly qualified people in Bristol who make literally a fifth of my salary yet for some reason do not want to move to London.
Initial HR filter is to weed out the DDOS of a million CVs on a job ad... Look for a backdoor. Friends, neighbors, Meetup, colleagues, online forums such as Twitter or Discord.
It's not just FAANGs that are offering TC that high in London. Have a look at levels.fyi if you want to see some numbers. Possibly not as prevalent nowadays unfortunately.