Sorry Moridin didn't catch this thread. I can't really add to Epona and Donuts comments other than to say sound advice. I won't give you any of my own as your sure to top up arrested, incredibly drunk or in some other form of trouble. I hope you enjoy your stay buddy and let us know the dates and area in which you are staying. London and its suburbs cover a big area and just because you have a London postal address it doesn't necessarily mean you'll be that close to the City itself. Keep us posted on the above score and we'll all do our best to advise.
This may still be worth a look at mate -
http://www.londontown.com/
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One love, peace.