Stolen bikes

The Metropolitan Police run a cycle crime unit called The Cycle Task Force who can be found through the Metropolitan website. If you see your bike or know where it may be after a theft you can contact them and they have "protocols" for retrieving stolen bikes.

They do not advise trying to retake the bike yourself in case the situation escalates.
They aren't a rapid response unit and watching what you believe to be your bike slip through your fingers can be very frustrating.

Also see the first post in this thread:

http://www.lfgss.com/thread52193.html