Yes it's a lovely car, madam, I nicked it myself

All Wendy Carmichael wanted to do was buy a used car for £2,500. Simple enough, until she sensed the sellers becoming impatient. She agreed to buy the car, but did not feel happy. "I sensed something was wrong. I was told I could check the identity of the vehicle. It turned out that the number plates were false, they had been switched with another car. I was in the process of buying a stolen car."

Wendy was lucky. Had she gone through with the purchase, not only would she have lost all her money, but the car would have been returned to the original owner, or an insurance company if a claim had been paid.

The company Wendy turned to for information about the suspicious car was HPI Autodata, and according to figures it has just released, as many as one in three vehicles for sale is a "ringer"or stolen. "Ringing" is at the root of the most car crime in the UK.

First of all the criminals buy an insurance write-off from a salvage yard. Once they have that car, complete with registration document, they commission, or carry out the theft of an identical vehicle, which is a dead ringer for the write off. All the criminal has to do is transfer the identity of the write-off with that of the stolen car, which effectively disappears.

At its simplest the criminals can simply swap the number plates, but in order to make the deception more convincing they must also transfer the vehicle identification number (VIN). The VIN is a unique sequence of 17 digits stamped on to a plate which is riveted to the car body and also stamped directly on to the metalwork. This is when it gets a little more tricky, and in some cases the criminals perform more serious surgery known as "cut and shut". Here the sections of the written-off car containing the VIN stamp are cut off and attached to the stolen one. It is the classic scam of joining two cars together which is not just dishonest, but downright dangerous as cut and shuts self-destruct, even in minor collisions.

HPI Autodata has the statistics to prove that the "ringing" problem is getting worse. As a company it offers the facility to both trade and public to check national databases and establish whether the used vehicle is stolen, still on finance, or a rebuilt insurance write-off. Originally it relied on the registration number as a reference point, but now it includes the VIN as part of its new service. "In the last week alone almost 400 checks were made and over third of these cross-checks revealed that the vehicles could be `ringers'," said Nicki Webster, the marketing manager.

Insurance companies must take some responsibility. When insurers sell a write-off, the identity of the car goes with it, including the V5 registration document. Even though they are under a duty to realise the maximum amount of money to keep our premiums down and pay out claims, leaving the wrecks liable to "ringing" only encourages theft and ultimately pushes up premiums anyway.

This vicious circle could be broken if every write-off had its VIN numbers removed and the V5 sent to the DVLA and recorded as scrapped. Only a handful of insurers are operating such systems. The motor industry has been aware of the problem for some time and now stamps the VIN number in creative and more obscure places.

So what chance do ordinary punters stand when they are out innocently shopping for a used car? Well, HPI Autodata can help, so can an inspection by a professional engineer, but first there are plenty of common-sense precautions. The car may be advertised at a temptingly low price. Beware, also, of sellers in a hurry, pressuring you into making a quick decision. Buying from a reputable and established dealer who makes all the VIN checks has never seemed so attractive.

In every other circumstance though, locate the VIN plate, which can usually be found under the bonnet riveted to an inner wing, and check it against the V5 registration document. There is also an engine number which is stamped on to the block itself and should be cross- referenced in the same way.Finding where the VIN is stamped on the bodywork can be more of a challenge, so telephoning the manufacturer ends the mystery.

But matching the numbers to the available documentation, which includes recent MoT certificates, is not enough. It is also important to look carefully at all the numbers and ensure the VIN has not been interfered with. Give-aways are disturbed rivets, uneven stamping of the digits and any other signs of disturbance around those numbers, such as scratch marks, cuts and fresh paint.

HPI Autodata: 01722 422422. Cost for each check £25.