It depends OP. I was on MN yesterday having a moan about house prices and schools, but I think DP and I would genuinely leave the country before living elsewhere in the UK (him particularly, but I'm not far off).
Why?
We're both foreigners, and London is a great place to be a foreigner since no-one cares and there isn't ever a sense that you're an outsider. I don't mean to paint the rest of the UK as some some of Deliverance-style backwater, but I haven't felt welcome everywhere we go.
Access to culture: it's not like we swan off to the ballet or theatre every week, but we both like art-house films, concerts, exhibitions, and there's just cumulatively more happening in London. (Sometimes when overworked City types say this I feel like asking when the last time was that they actually made it to a cultural event but, well, we try.)
Jobs: I can work anywhere, but DP is a software developer and there are a lot more jobs going here. Salaries are, for us anyway, high enough to make up for the higher cost of living. (When I last worked for a law firm as a very junior associate, I was on £100k. That is unheard of outside of London.)
I am not particularly interested in postcodes or gloating about where I live, but feel that my/our use of amenities justifies the sacrifice, for now.