DVLA registered companies are selling vehicle licence plates to drivers without carrying out proper checks, a BBC investigation has found.
In some cases this has led to registered owners facing fines or arrest when it wrongly appears their vehicles are involved in crime.
One Birmingham firm made cloned plates in 10 minutes, with no log book checks.
When confronted, another licence plate retailer said the business did not "deliberately flout its obligations".
A vehicle user should be asked to prove their name and address and their right to use the registration number when they ask for a new licence plate to be made.
Failure to make these checks can lead to companies producing plates showing licence numbers the buyers have no right to use, leaving them free to drive a vehicle bearing the identity of someone else's car.
Neither the DVLA nor the police could provide an accurate figure for the number of cloned cars on the road, but told the BBC it was a significant problem.
Adam Shirley, from Camberley in Surrey, has received 18 letters demanding a total of more than £1,000 in fines after vehicles bearing his licence number picked up parking tickets in places he has not been to. Most came from the London borough of Wandsworth, 30 miles away.
"I'm kind of scared that someone will commit a bigger crime using a car with my licence plate on it," he said.
What rules are there?
- You can only get a number plate made by a registered supplier
- The supplier will need to see original documents that prove your name and address
- The dealer must also see original documents showing you are allowed to use the registration number
- Details of registered suppliers and the documents you can use are available on the government website
Two Birmingham retailers both failed to demand to see a log book, despite it being a DVLA requirement for all registered retailers, when a BBC undercover reporter asked for number plates to be made.
One, Numberplatesrus, supplied three cloned plates and was able to produce a set in just 10 minutes.
An employee claimed to have "software with DVLA" that "comes up with your name and reg and stuff" upon payment.
The DVLA said no such system existed.
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At another shop in Handsworth, C&C Car Spares and Accessories, nobody demanded to see a vehicle log book, and staff made a copy of Mr Shirley's already-cloned plates and also supplied plates from a BBC-registered vehicle.
In a letter, C&C Car Spares and Accessories accepted there had been "some failings" after it was secretly filmed selling plates without the required checks, but said it felt "deliberately and purposefully duped".
The owner said he would "remain vigilant to ensure he is not placed in this position in future".
A DVLA spokesperson advised motorists who believed their plates had been cloned to contact police and said it undertook "spot checks to ensure suppliers producing number plates are doing so correctly".
You can see this story in full on BBC Inside Out in the South, South West, East and West Midlands regions at 19:30 BST on BBC One on Monday 10 September, or via iPlayer for 30 days afterwards.