Criminals are copying or stealing registration plates and using them to enter areas such as the London congestion charging zone without paying.
Any fines incurred are sent to the fleet manager running the car the number plate actually belongs to.
Fleet managers at the London West regional meeting of ACFO, the fleet operators association, were told that getting refunds from the authorities was long-winded and difficult.
One fleet operator revealed she had six cloned vehicles.
She said: ‘We have spoken to the Driver and Vehicle Licensing Authority and asked if they can inform us if there is more than one vehicle listed under one registration.’
Although there is no simple solution in sight, members heard that at least the congestion charge was being lifted over the Christmas period. It will be suspended from December 24 until January 2.
Police have said thefts of number plates are rocketing, with 6,500 alone in the London area since April.
Recent laws that require the presentation of a V5 document for replacement plates, and the increasing use of automotive number plate recognition equipment (ANPR), mean that thieves are simply unscrewing plates from parked cars.
Once they re-attach them to a similar spec machine, they can then rack up fines and charges to someone else’s vehicle.
Des McCann, director of network and operation for Budget Car and Van Rental, said there was very little the industry could do about such crime. He said: ‘Where we can take action is when a vehicle is returned missing one or both plates following an accident.
‘We should question the circumstances of the incident when it is clear the details do not stack up. It would be unusual for both plates to go missing on any type of accident, especially a minor one. If suspicious, we should pass on the details to the police.’
The biggest problem, he added, was the administrative burden that such incidents bring.