EDIT: i'm not trying to be arsey here, just pointing out where you could help yourself out for next time. Which is in itself a shame - we shouldn't have to lug around ££s and KGs worth of locks just to leave a bicycle in a public area in daylight for a couple of hours. But as a wise man once said, "this is London my friend".
Sorry for your loss, hopefully you may get it back.
Next time, please consider using something more secure than a £20 cable lock to secure it with.
Check this thread for some great advice:
http://www.lfgss.com/thread17938.html
EDIT: i'm not trying to be arsey here, just pointing out where you could help yourself out for next time. Which is in itself a shame - we shouldn't have to lug around ££s and KGs worth of locks just to leave a bicycle in a public area in daylight for a couple of hours. But as a wise man once said, "this is London my friend".