Whereabouts in London will you be going, and when?
There are dozens of meetings in London every day (some of them won't be on during the olympics, because the people who own the places where they are have put the rent up for the duration) and I've only been to three of them, and only once. Alas, I don't have my 'where to find' with me at the moment.
But I'm sure that, wherever you go, you'll have no problems finding a meeting.