Drivers are clocking their cars to avoid excess mileage penalties on fixed mileage leases, according to valuations guide Glass's.

Drivers are increasingly turning to mileage adjustment companies who use specialist equipment to artificially reduce the number of miles showing on the odometer. Because most of the vehicles involved have been supplied new and are less than three years old, there is no MOT certificate and often only one service stamp, so the paper trail doesn't reveal that the mileage has been altered.

Rupert Pontin, head of valuations at Glass's, said: "Some drivers facing a PCP returns charge may consider clocking as an easy way of avoiding payment but their actions are illegal.

"The issue tends to come to light when the car is prepared for sale either by the original dealer or another who has subsequently bought the car, probably at auction. When they plug the vehicle into their diagnostic rig as part of their standard vehicle preparation procedure and, depending on the model, an error code will show what has occurred.

"This places the dealer in a very difficult position because it is next to impossible to prove when the clocking took place. It is often too late to take any action against the driver because the PCP returns paperwork has already been processed and, anyway, they will usually just deny that they have clocked the car."

Pontin said that Glass's had come across several cases of this type in recent months being reported by both dealers and motor auctions.

He said: "At this stage, it is very difficult to say how widespread this practice might be but we are certainly seeing an increasing amount of industry ‘chatter' about the subject and it is considered a growing problem, especially as PCPs continue to massively increase their market penetration."

There was no easy answer to the problem, Pontin explained, although closer regulation of mileage adjustment companies was one potential route.

He said: "Mileage adjustment of electronic odometers exists for all kinds of good and perfectly legal reasons, such as to correct the reading on a car that has had its dashboard replaced or where the odometer has failed. However, while we have no reason to believe that the majority of operators are anything other than ethical, there do appear to be at least a few who will reduce your mileage without asking many questions.

"One solution is for dealers to check vehicles for clocking as part of their standard PCP returns procedure. This would effectively ‘prove' that the vehicle had been clocked during the contract period, placing the onus on the driver for what is, after all, a form of fraud and quite a serious crime."

Pontin added that clocking by dealers - once considered prevalent in the motor trade - had effectively become almost unknown in the 21st century because of the strict penalties that existed.

He said: "We have come across very, very few cases of dealer clocking in recent years and, in essence, the practice had almost died out until now - but it does certainly appear to be back."