Travelex, the world's biggest operator of bureaux d'echanges, has warned that the foreign exchange retail sector will be hit hard by the introduction of the euro.

The UK group also said that travellers risked being stranded without cash at airports in the first days of the new currency because of a shortage of euros in airports' cash machines.

Clive Kahn, Travelex's chief financial officer, said sales of foreign currency in Europe - believed to be worth more than £10bn ($14.4bn) a year - would fall by at least 60 per cent next year after the arrival of the single currency.

Bureaux d'echange operators have been expected to be hit by the disappearance of 12 national currencies from January 1 but few reliable estimates of the reduction in the foreign exchange market had been produced so far.

"We expect the size of the market to be reduced by at least 60 per cent. The introduction of the euro will have an impact on our European operations," said Mr Kahn after a press conference by UK law enforcement authorities on the security risks of the euro.

Travelex's 400 European bureaux d'exchange process some £360m of currency a year in the eurozone.

The chief financial officer urged travellers from outside the eurozone to obtain euros before they leave because cash machines at airports could be empty in the first days of the new currency. "In the very initial period there will be some shortages. There will not be the same level of confidence that the ATMs at the airports will be stocked," he said. Empty ATMs could mean travellers would be unable to pay for transport from the airport to their destination.

Mr Kahn advised travellers from outside the eurozone to use "a mixed purse" with some euros obtained before departure, some travellers' cheques and some of their national currency.