Drivers who leave their engines running while clearing ice and snow from their windscreens could face being prosecuted under the Road Traffic Act.
Police in Leicestershire have warned motorists that not being in their car when the engine is on is an offence known as "quitting" and could lead to a £30 fixed penalty notice.
Head of the Roads Policing Unit at Leicestershire Police, Inspector Gill Lewis, said: "With automotive security getting better all time, it's becoming very difficult to steal a vehicle without having the keys.
"Thieves are wise to this and target people who leave their cars running with keys in the ignition.
"You wouldn't leave £30,000 in the road for someone to steal. Yet it's surprising how many people will leave their cars defrosting unattended at the side of the road.
"If you are defrosting your car, make sure it is not left unattended."
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