Moved to Glasgow for a higher salary than I had in London, and where rent is 1/3 of the price.
There's Edinburgh, Manchester(home of the bbc) (ranked as two of the best cities for tech in the UK, manchester for media city), Bristol, Bath, Newcastle, Cambridge. All good salaries and likely to save more money than in London.
There's some startup hubs in Edinburgh that are really friendly - i'd go put your cv in there. One is called "codebase"
It's swings and roundabouts, Cardiff isn't as happening as London or even Bristol (certainly food wise) but money certainly goes further. The worry is if I lose job at 'Thisbigcorp' there are fewer places that would offer a package this good.
Working from home is fairly standard a couple times a week here too.