Also, whenever I see these programs with a ton of mentors (http://ignite100.com/view/mentors/) I think "quantity over quality". Look at YC: a tiny team of people. You don't need 50 mentors, you need three good ones. Also, Ignite 100 looks like it is a rebranding/relaunching of a previous program called The Difference Engine. I'd like to see some successes from that before judging this program.
And there are quality VCs in London (e.g. Accel has a major office here).