Tour operators selling foreign holidays must be licensed by the Commission for Aviation Regulation (CAR). However, a number of leading travel companies, including Concorde Travel, CIE Tours International and the Irish arm of Lastminute. com, have seen their licences lapse. Well-established travel agents, such as Swansea Cork Ferries, Usit and Trinity College Student's Union Travel, are also temporarily affected, as is the Garda Holiday and Travel Club.

The commission, headed by Cathal Guiomard confirmed people booking holidays with a tour operator or travel agent without a valid licence are not covered by bonds managed by the regulator, even if the tour operator subsequently receives a licences . . . licences are not issued retrospectively.

The bonds are supposed to cover the costs of repatriating customers of tour operators and agents that go out of business. Customers could now be forced to pay for their own transport home and would not be legally eligible for a refund if an operator went bust before the holiday commenced. A CAR spokesman could not explain why operators, with expired licences, are being permitted to continue selling holidays.

A number of operators contacted by the Sunday Tribune expressed surprise that their applications had not yet been processed. It is understood that all the travel companies listed as having expired licences had already applied for their renewal before their licences lapsed.

Lastminute claims that bookings made online are bonded under its tour operator's licence. The regulator told the Sunday Tribune that while a bond may be in place, it is not valid unless a tour operator's licence has been issued.

A CIE Tours spokesman said that it was essential that the regulator and operators should not permit the current situation to reoccur and stressed no-one has booked a holiday with the firm in the past two weeks from Ireland to a foreign destination.

Dermott Jewell, chief executive of the Consumers' Association of Ireland, described the situation as "unacceptable". "This goes against every single thing that would have brought about the necessity for the regulator, " he said. "The fact this could happen could easily be identified in an audit. It's so poor it's hard to believe."