The Commission for Aviation Regulation and Irish Aviation Authority (IAA) are clamping down on private helicopter owners running illegal taxi services at events such as the Galway Races and the Slane music festival.

The use of such helicopter shuttle services has grown exponentially in recent years and the commission is investigating at least one helicopter owner in the State who is alleged to be running a business carrying paying passengers without a licence, insurance cover or adherence to the commission's safety requirements for commercial craft.

A spokeswoman for the commission confirmed her agency was notified by one of the larger helicopter operators, Celtic Helicopters, "a couple of months ago" about the alleged illegal carrier.

Celtic Helicopters conducted its own surveillance on the helicopter and its owner and has provided video and invoice evidence backing up its claim that the operator is running an unlicensed business.

The commission's spokeswoman said the investigation was "a work in progress" and that when it was complete, a file may be passed onto the Department of Transport where any criminal charges would be considered.

Although just one helicopter owner is under investigation, it is understood a number of alleged illegal carriers have been brought to the commission's attention by different players in the Irish aviation business. As journeys are often paid for in cash, proving a business is operating can be difficult.

Yesterday the commission placed adverts in national newspapers warning craft owners and members of the public that only licensed operators are permitted to carry paying customers.

Celtic Helicopters director and chief pilot, Mr John Barnicle, told The Irish Times that illegal carriers had been operating in the Republic for around 10 years. He said their increasing activity was taking millions in business from reputable operators adding that the illegal outfits paid no tax.

Mr Barnicle said his company spent €5,000 collecting evidence against the helicopter owner currently under investigation. It is on the basis of this evidence that the commission and IAA are conducting their investigation.

"The people running these operations don't seem to realise what they are putting on the line," Mr Barnicle said.

"Unfortunately it is not until after an accident happens that they will realise what they are doing. If an accident were to happen while they were carrying paying passengers, nobody, not even third parties, would be insured if anything goes wrong."