The government is being urged to clamp down on untaxed foreign vehicles after the RAC warned they were costing the UK millions of pounds a year.
About 60,000 foreign vehicles are registered with the Driver and Vehicle Licensing Agency (DVLA) every year.
However, the RAC said an estimated 15,000 others are not – the motoring organisation said this amounts to about £3m per year in uncollected tax.
The government said it would shortly announce plans to combat the problem.
The DVLA was unable to verify how many foreign vehicles coming into the UK are not registered, but did not contest the RAC’s figures.
The RAC’s head of external affairs Pete Williams said the situation was “beyond belief”.