One of these forums would probably have more London based members than we do (but stick around on this one, too):
http://www.anothercyclingforum.com/index.php
http://www.cyclechat.co.uk/forums/index.php
http://www.bikeradar.com/forums/

I've heard that folding bicycles are getting popular in the UK, probably because so many people share your predicament.