So, you catch a 'thief'...

Isn't the advice that the police give that:

If you see a crime in progress to call 999.
If the crime has already taken place, then you phone your local station.

I'd phone 999 anyway, cos they are duty bound to record it and act upon it.

get real - in london? do you think they'll turn on the blue lights for a possible stolen bike? unless there is real and immediate danger of harm to a person, they will take days.