When I was at school, the local plod would periodically check the bikes in the bike sheds, and since in that era we didn't seem to lock our bikes to anything (just a lock around the rear wheel and frame), they'd then remove all the unsafe ones, and require whoever they belonged to, to come and pick them up.
Presumably they then explained to them what was unsafe, and told them to walk home. Mine never got taken away, so I'm not sure exactly what happened!