What to do if someone has locked their bike to yours?

Call the police again and ask to be in touch with the cycle task force?

surely this whole thread is within the remit of the Cycle Task Force?!

A new, 30-strong Police Cycle Task Force hit the streets of London today, as London's police forces, the Mayor and Transport for London (TfL) published a draft plan for tackling cycle theft and vandalism in the Capital.

enquiry sent about this very scenario (!)..

.. keenly awaiting delivery of the Cycle Task Force Locks-in-a-twist hotline, :-)