The legal battle between Aer Rianta and the airport regulator Mr William Prasifka has cost the State EUR5 million so far, it was revealed yesterday.

In answer to a question from Fine Gael transport spokesman, Mr Denis Naughten, the Minister for Transport, Mr Brennan said the costs - so far - ran to €5 million.

He was speaking during a meeting of the Joint Oireachtas Committee on Transport. However, sources last night said the €5 million was likely to be exceeded, with Aer Rianta currently looking for leave to appeal a recent decision that went against it in the High Court involving Mr Prasifka, who heads the Commission on Aviation Regulation.

"It is incredible that two arms of the State, both of them under the authority of Minister Brennan, could end up in court with the taxpayer and consumers ultimately picking up the €5 million bill for this case, which was ultimately lost by Aer Rianta," Mr Naughten said.

"At a time when the Government is implementing major cutbacks, and we have State agencies taking each other to court, surely some alternative mechanism should have been found rather than the taxpayer having to foot the bill," he added.

It is estimated that the costs alone in the High Court case for Mr Prasifka's side amounted to €2.2 million, with Aer Rianta's costs at least matching these. If Aer Rianta gets leave to appeal to the Supreme Court the costs will rise further.

Mr Naughten said the blame resided with Mr Brennan, who should not have let the case go to court. However, department sources pointed out that the case began before Mr Brennan entered the department.

The case concerned the extent of Mr Prasifka's authority to control the charges levied by Aer Rianta on airlines for using its facilities.

Aer Rianta wanted to set charges at a certain point in order to fund a capital expenditure programme of €1.28 billion.

The case also concerned the process used by Mr Prasifka to evaluate Aer Rianta's charging structure.