Finance information provider HPI and valuation company Glass’s have worked together to highlight the dangers of buying a ‘clocked’ car, a problem that affects one in 20 cars.

‘Clocking,’ or reducing the mileage of a used car in order to increase the price is a growing practise, and HPI’s figures revealed a 10% rise between 2007 and 2012 in cars being clocked, and a further rise of 3% in 2013.

The company estimates there could be as many as 486,000 vehicles with false mileages on UK roads.

Senior consumer services manager of www.HPIcheck.com Shane Tesky said "Too many used car buyers ignore the threat or just aren’t aware of the risks from fraudsters who use ‘clocking’ to alter a vehicle’s mileage."

At the same time, figures from Glass’s show a three year old Volkswagen Golf with 90,000 miles on the clock worth £8,870 would sell for £11,060 if the number of miles were halved.

The figures also demonstrated a 2011 year old BMW 5 series with 120,000 miles on the clock would be worth £13,380. Reducing the mileage by 50,000 would add around 19% to the cars value.

Similarly reducing a £16,360 2011 Mercedes C-class with 90,000 miles on the clock’s mileage by half would take the value up to £18,600.

HPI said these figures revealed the true potential costs facing unsuspecting buyers in the face of unscrupulous sellers who could adjust the mileage of a car.

Speaking to Motor Finance, Tusker said the companies focus was on newer cars because that was where HPI was seeing an increase in clocking. He said "It relates to the MOT history becoming a little bit easier for people to get their hands on as cars get older, and also if you clock a ten year old car by 50,000 miles, the return for you isn’t going to be as good as if your clocking an older car."

Specifically, he warned: "Cars coming out of company fleets that would have significant mileage are prime targets for clockers. They can pick them up at auction for a competitive price, work their magic and get a return of around £2,000. And the service history tends to get lost of forged in the process."

Andrew Jackson, head of analytics at Glass’s said in a statement: "Clocking is a serious issue – dodgy sellers are making a fast profit at the expense of innocent buyers, but consumers could lose more than just money if they buy a vehicle they don’t realised has been clocked.

"Tampering with the odometer may lead to safety issues, especially if a vehicle appears as if it doesn’t need a service, when it actually does. The act of clocking could disguise the need for a major mechanical repair, leaving buyers with a hefty bill if something does go wrong."

Teskey added "We’re hoping that by exposing how much money buyers stand to lose, consumers will take greater steps to protect themselves. It’s almost impossible to spot a clocked vehicle just by looking at it, which makes an HPI Check a vital tool for buyers keen to avoid falling foul of fraudsters."