We (Songkick, yc s2007) have a floor of a warehouse just up the road from Silicon Roundabout. There are about 8 startups based at our place (including Habit Industries, also yc s2007).
This post gives a really measured, non-sensatinal view of what it's like to start up in London. We're really enjoying building Songkick here.. It's changed for the better even in the two years we've been starting up.
Btw - we have deskspace going at our place - see here: <a href="http://www.gumtree.com/london/17/50884217.html" rel="nofollow">http://www.gumtree.com/london/17/50884217.html</a>