If you didn't have to be in London, I'd highly recommend looking at Red Gate. They're, by far, the best company I've ever worked with: http://www.red-gate.com
I have an impression, the more senior you are the harder is to get hired by companies testing how good you remember some intricate [implementation] details from your CS courses.
nah, no worries, in a sense it was good. I noticed areas I need to improve and I'm happy to get to the on-site interview. If I got to that step I probably will be more confident with other interview processes.
Not to mention people who are self-taught...