Relations between Aer Rianta and Ryanair further deteriorated yesterday as the row between the airport management company and the low cost airline became increasingly personalised.

Responding to Ryanair's threat to withdraw from Dublin Airport by Christmas unless a low operating cost mechanism was established there, Aer Rianta claimed the airport's landing charges provided "excellent value for money" at £1.93 per passenger.

Mr Flan Clune, public relations manager, said that, over the past two years, the chief executive of Ryanair, Mr Michael O'Leary, had been paid £17 million in director's fees while Aer Rianta had received just over £16 million.

Mr Clune said that Aer Rianta had responsibility for running the airport as a viable entity. "We are not in the business of making millionaires out of private shareholders whether they come from Miami or Mullingar," he said. Mr O'Leary is originally from Mullingar, Co Westmeath.

British airports were putting up their landing charges by 15 per cent in a move approved by the Monopolies and Mergers Commission Mr Clune added. "All we have said is that we may have to put up our charges," he said.

He added that even if the £1.93 charge was doubled, which would not occur, it would still comprise a small part of Ryanair's total costs.

Studies had shown that Dublin was among the cheapest airports in Europe and that the rebate scheme was "the best available anywhere". Aer Rianta cited the Eagle Award received by it from the Irish Association of Travel Agents, which held the management company up as "a benchmark for other airports to copy" and added that the threat made by Ryanair's chief executive, Mr Michael O'Leary, was a familiar one.

"He made a similar threat last week in the Financial Times regarding Stansted Airport and one some time earlier to both Birmingham and Manchester airports," the company said in a statement.

Mr Michael Cawley, Ryanair's chief financial officer, said the issue for the airline was where the landing charge was "going" and whether it could get a long-term agreement.

"We need a cost base which is at or below what it is at the moment . . . We need that kind of stability to make the investment in resources here in Dublin," he added.

Ryanair had experienced logistical problems in Stansted and had cut back scheduled flights in Manchester because of high charges. "What we have said is, if we do not have a favourable decision by December 31st from our point of view, growth is going elsewhere and we will start to wind down the frequency of our flights."