With increasing international mobility and economic migration, AA Business Services is warning that the problem could get worse as the European Union expands.
Fleet managers taking on overseas workers are warned to be especially vigilant.
Many fleets struggle to identify whether the licences they are given are legal documents, as there are more than 110 different types of licence circulating across the EU.
The AA is receiving increasing numbers of enquiries about international licences and has found that several motorists hold invalid accreditation.
One driver from Croatia had been behind the wheel of his car for almost 15 years without a valid licence.
‘This is the tip of a very worrying iceberg as the EU continues to enlarge,’ said Paul Holmes, head of risk management at AA Business Services.
‘If you are a fleet manager, how do you know if the licence you have been provided with is legal? It may look bona fide, but you have no immediate way of telling without reference to another body such as ourselves.’