The police are warning fleets to be on their guard against fuel thieves after a spate of crimes in which vehicles’ fuel tanks were drilled and emptied.

The increase in the fuel theft from stationary vehicles is being blamed on the record price of petrol and diesel, which both now cost well in excess of £1.05 a litre.

This means an average family estate can contain £80 of fuel when its tank is full.

Last month 20 cars, which were parked up overnight in Oxfordshire, were targeted by thieves, who drilled into their plastic tanks to steal their fuel.

In addition to the lost fuel, which is untraceable and in high demand, the owners also had to pay an estimated £400 per car in repair costs, which involved replacing the damaged tanks.

Nobody has been arrested for the thefts, which Oxfordshire police blamed on “organised criminals” who knew what they were doing.

“While we can’t directly link the crimes to the rise in fuel prices, it is likely that there is a link,” DC Clare Routledge of Oxford Police Car Crime Unit said.

“Our advice to fleets is to be on your look out for suspicious behaviour, always ensure your vehicles are parked in well lit areas, and, if possible, with the fuel tank facing away from the street.”

Oxford has seen a marked increase in fuel thefts from parked vehicles.

Already this year, there have been almost twice as many reported thefts than for the whole of 2007.

And the problem is not confined to the Oxford area.

A Southampton-based LCV driver was reportedly targeted twice.

His van suffered £1,000 of damage as a result of thieves drilling through the diesel tank and draining it.

The incidence of drilling directly into plastic tanks is a direct response to the widespread use of anti-siphoning devices and the growth in the use of plastic rather than metal.

It is estimated that 85% of new vehicles in Europe now have plastic fuel tanks.

These tanks are cheaper, safer and lighter than the metal tanks they replace, although the rise in fuel thefts may force manufacturers to rethink their positioning and accessibility.