I didn't say it was "below average", I said it was "below the average [in SF/SV]". http://www.prospects.ac.uk/applications_developer_salary.htm claims the average salary for a senior developer is £50,000. I'm going to assume that that's the average across the U.K., so lets allow 33% more for being located in London (33% is what I see commonly thrown around for SF/SV vs. other large US city). If we assume a generous currency conversion rate of 1.6, that works out to ~107k USD. That's extremely low for a senior software developer in the Bay Area. And London isn't any cheaper than SF ...