Not OP, but I think that is pre-tax. Most salaries I've seen are quoted in gross terms.
As far as living in London, a lot of people have roommates/live in flatshares to save on rent or live in the commuter towns around the M25 belt (big highway surrounding London).
Startups in London offer significantly less salary than SF/NYC. You can earn by being a perm employee in finance or contracting.