Motorists have been warned to be on their guard for opportunist car thieves after more than 50 vehicles were stolen while people were defrosting their cars.

The so called “frost-jackers” took the vehicles from under noses of their owners who had walked away from them while the engines were left running to warm up.

The crime craze has swept the West Midlands with an estimated 50 cars and vans being taken by thieves on the prowl during the cold snap.

The latest anti-theft technology means that modern cars cannot be stolen unless thieves have the keys and police are frustrated that motorists were making it easy by leaving cars running.

And it is not only the owners of luxury models that are falling victim. While a number of BMWs, Audis and Mercedes have been stolen, thieves have also taken Vauxhall Astras, Peugeots and a VW Jetta.

Senior officers have also said insurance companies were unlikely to pay out in such cases.

Police have now stepped up special frosty morning patrols across the Midlands with officers taking keys from vehicles left unattended.

Chief Supt Jon Hesketh, from Force Intelligence, said: “People think it’s fine to leave cars unattended for just a moment, but a moment is all it takes for the car to be stolen. Opportunist thieves are aware cars will be left unlocked to warm up and they will take your car if given chance.”