One in 20 cars has been clocked

* 'Clocking' up by 10% over past five years * One million cars found to altered in 2011 * Private sellers clocking cars, too...

One in 20 cars has been clocked

The number of clocked used cars in the UK has increased by 10% over the past five years, according to vehicle history expert HPI.

More than one million used cars checked by HPI in 2011 were found to have had their mileage altered.

HPI also revealed the problem extends beyond unscrupulous dealers, to private sellers who are clocking cars to increase resale value. Some with lease deals are tampering with readings to avoid breaching their contract.

Clocking can increase the vehicle's value for sellers; taking off 1000 miles can add between 100 and 400 to the price.

Although its not illegal to alter a cars mileage, it is illegal to hide this information from a potential buyer. This is compounded by the fact that around 50 'mileage correction' companies are operating in the UK.

Kristian Welch from HPI commented on the findings: Its alarming to think that people are exploiting new ways to reduce the mileage on a vehicle to put hundreds or even thousands onto the pricetag.

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.