If you refuse to work for finance in, say, NYC, then
you'll be unemployed often because that's a lot of what's
out there.
List of tech companies in NYC: http://nytm.org/made-in-nyc/grid
Map of tech companies in NYC: http://mappedinny.com/
This is much of why I think the future is elsewhere. Not NYC, not the Valley. It's going to be somewhere where it's possible for a normal 40-year-old to have a career as a programmer (not a manager who occasionally codes) because it genuinely takes decades to become great at this stuff. Most of these "social" apps could be built by anyone, but if I needed a medical device, or an extremely high-performance numeric library, I'd rather the code be written by a seasoned gray-haired guy who understands technology at a deep level than by the sorts of people in charge at a lot of the startups where I've worked.
Sure if you work in finance you can earn more, but it's about funding a more lavish life-style than a necessity. Pretending anything else is insulting to the millions of families who are living on less.
Do startups generally pay below market? Yes. Is finance even more lucrative? Yes. But you certainly won't be "unemployed", as you suggested, if you don't work in finance.
Code quality problems aren't limited to finance and the people in finance are, on average, somewhat better than (at least) the NYC startup crowd. (There are good people in each, of course, and bad.)
I don't know the UK scene, but if you're certainly moving to London, you shouldn't rule out finance. Even though there are some terrible financial firms out there, I don't think that the whole set of financial companies is, as a category, any worse than other businesses (including startups). Those blue-sky R&D jobs (to which finance might compare poorly) are so rare and inaccessible to our generation that one can assume them not to exist in the corporate world (at least, not in the U.S.).