THIEVES have been preying on motorists who leave their keys in the ignition and engines running to defrost their cars.

But there is more misery -- those who have had their vehicles stolen in this way not only invalidate their insurance but they could actually be FINED.

PC Steve Cottam, an instructor at the Greater Manchester Police Driving School, said leaving a vehicle unattended on the road with the engine running means the owner is committing the offence of "quitting a vehicle." And that carries a £30 fine.

PC Cottam said: "You can leave a vehicle with the engine running if you leave a qualified driver in the passenger seat. Leave a non-driver, including a child, and you are breaking the law."

He said certain vehicles need to have the engine running to function correctly such as dustbin lorries and cement mixers.

Police traffic cars also leave the engine on to operate the flashing lights at accident scenes.

But these vehicles are specially adapted, PC Cottam said, and are left running without the key while unattended.

If someone tries to steal one, the engine will cut out.

There has been a spate of similar thefts in recent weeks and police have repeatedly warned motorists about the risks of leaving their vehicles running with the keys in the ignition.