Around 400,000 used cars have been 'clocked' before they are put up sale, according to vehicle check experts HPI.
Clocking entails reducing the mileage on a car's odometer. This can increase the vehicle's value taking off 1000 miles can add between 100 and 400 to the price.
'Clocking is a more common occurrence than people might think,' said Nicola Johnson, consumer services manager of vehicle check experts HPI.
She warned that modern cars hide the signs of clocking better than older ones, saying: 'Recent years have seen dodgy sellers come up with new methods of clocking, so it's harder than ever to identify a tampered car by simply looking at it.'
She also pointed out that there are around 50 'mileage correction' companies operating in the UK. HPI says that altering mileages is not illegal in itself, but not declaring it has been changed to a potential buyer is against the law.
How to spot a clocked car
Here's what HPI recommends:
• Look out for abnormal amounts of wear and tear
• Check the service history and look at the mileage by each service stamp
• Speak to the previous owner the details should be on the logbook
• Check the mileage when you first drive a car and then again when you pick it up if you have chosen to buy it some sellers have been known to wind the mileage back and then reset it to its original value when a deal is complete.