Thousands of untaxed foreign cars on British roads mean the Treasury is missing out on millions of pounds each year, the RAC has said.
Around 60,000 non-UK vehicles are registered with the Driver and Vehicle Licensing Agency (DVLA) every year but an estimated 15,000 are not registered, the RAC said.
It means that around £3 million in vehicle excise duty (VED) is not being collected each year, the RAC added.
The RAC said that under current regulations visiting non-UK cars must be registered with the DVLA once they have been in the UK for six months.
Foreign drivers must then pay a £55 first registration fee, ensure they have paid VED, obtain an MOT if the vehicle is over three years old and in some instances pay VAT.