From what I've seen, London studios are offering competitive salaries, but it really depends on your portfolio quality and experience level. The cost of living is definitely higher there though.
I recently made a similar move and can share some insights. London salaries for CG artists vary quite a bit, but most studios are pretty transparent about being competitive based on experience. I'd recommend looking at specific job postings to get a better sense of what's available. Check out https://cgaward.com.ua/work.html - they have some London-based positions listed that might give you a good baseline for salary expectations.
--------------------- КиСлоТныЕ КлаБеРы РуЛяТ - the Acid has gobbled up a brain