Stolen bikes

I think I may have seen those thieving kids with a/the stolen bike(s) yesterday at the corner of Kingsway and Theobolds Road. Two kids all dressed in black with big hoodies riding along in a hurry dragging another bike with bits falling off it (a light and a rear mud guard) which they didnt stop for. That was what drew my attention. Didnt know what to do, there were no other cyclists about and I didnt think the police would have cared about my sighting. Was quite upset about it when i got home.
With a crime evidently in progress, you should call 999. In that case, it's fairly easy for the police to take effective action, although they frequently arrive too late. Their response obviously also depends on what else is going on at the same time.