There are quite a few startups and companies in other areas like Edinburgh, Manchester, Leeds. They are still big (and somewhat) expensive cities but you can lower your cost of living.
But they pay pennies compared to London. What you save on rent you lose on income.
I get a lot of recruiter spam from UK recruiters, but truth be told, don't think I've ever got an email where the minimum offered was lower than £45k for London while for anywhere else the maximum range was £45-50k
