The RAC urged motorists to hide valuables, travel with the doors locked and not to stop if 'bumped' by another vehicle. Owners of BMWs, Mercedes and Jaguars were advised to be particularly alert as thieves are believed to have targeted such cars on the assumption that their drivers would be more likely to be carrying cash and valuables.
'We don't want to over-alarm people but they should be aware of the dangers. Thieves look for the little mobile phone aerial which tends to be on expensive cars. It's not the 1970 Vauxhall they go for,' Edmund King, RAC campaigns manager, said.
In separate incidents, robbers threatened to kill an antiques dealer with a knife before escaping on the M6 with items worth pounds 100,000, while a businesswoman in a white BMW was rammed on a rural road in Wales and robbed of wages she had collected from a bank.
Earlier this week a man driving through Middlesbrough was robbed of cash when his BMW was rammed and Mina Mullins had jewellery worth pounds 70,000 taken at gunpoint after she was stopped on the M25 in her Mercedes.
Higher value cars have been the target of gangs in west London, who have attacked more than 20 stationary vehicles in heavy traffic on the Westway.
Criminals in south-east London have used pedestrian crossing lights to stop cars before robbing their occupants. More than 20 incidents are believed to have occurred on the Old Kent Road within a month.
In yesterday's M6 incident, a 55-year-old antiques dealer was repairing a puncture on his G-registered Citroen early in the morning when a van pulled up behind him on the hard shoulder in Staffordshire. One man pinned him to the ground, drew a knife across his face and held the blade to his throat. The two heavily-built, middle-aged men escaped with five boxes of antiques, including a Georgian candlestick worth pounds 14,500.
A 'substantial' reward is being offered for information leading to the arrest of the gang who rammed Valerie Williams's car near Chepstow on Thursday afternoon.
Mrs Williams was forced to stop by a stolen Citroen and then rammed by other gang members in a Ford Capri. Three men in blue ski-masks leapt out of the vehicles, smashing crowbars and a truncheon on the roof of her BMW.
She was forced to hand over a bag containing thousands of pounds in wages for employees at her plant hire firm.
She said: 'One ran to the passenger door and another to the front of the car, and one to the driver's door and he tried very hard to break the glass. It has reached a very serious point when you cannot drive along little side roads in the daytime in safety. I would say to any woman to keep the doors locked.'
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