The secretary general of the Department of Transport is investigating the leak of a Cabinet memo about Aer Rianta to the Labour leader, Mr Pat Rabbitte.
At first the Taoiseach, Mr Ahern, told the Dáil that the Garda had begun an inquiry into how Mr Rabbitte obtained the confidential document, which showed the opposition of the Minister for Finance, Mr McCreevy, to legislation on the break-up of Aer Rianta.
The Taoiseach said: "A Garda investigation commenced this morning to find out how deputy Rabbitte got this document, whether it was a document that was taken, given over, stolen or whatever. It will be investigated in due course."
He later clarified that it would be investigated "in the first instance" by the secretary general of the Department of Transport.
"If the secretary general feels it has to go further, then obviously it would be a matter for the Garda."
Mr Ahern also insisted during an unruly Dáil session that Mr McCreevy "is fully supportive of the restructuring measures". He said the Minister had requested that important issues such as capitalisation, the transfer of debt, and the future of subsidiaries and employment should be addressed before legislation is finalised.
During a renewed row in the controversy over the proposed break-up of the semi-State company into three stand-alone authorities, Mr Ahern confirmed that the leaked document was a Government memorandum and it was the first one that had "vanished from a Department".
Mr Rabbitte said there were "more useful purposes that the Taoiseach might put gardaí to, rather than prohibiting this information entering the public domain". Mr Ahern said that because it was a Cabinet memo "it is a different issue".
When the Labour leader said he had never made any reference to the document being a Government memorandum, the Taoiseach said: "Unfortunately for you deputy Rabbitte, the text you used was the text that was in the Government memorandum only and not in the other literature."
Mr Rabbitte replied: "You missed your profession. Your calling is obviously as a detective." To which Mr Ahern retorted: "You shouldn't be so smart in quoting it exactly."
The Minister for Transport, Mr Brennan, intervened to ask Mr Rabbitte where he got the memo. The Labour leader replied: "Never mind where I got it. If you want to ask questions, I might ask you questions about what you got from Michael O'Leary."
The Minister for Communications, Mr Dermot Ahern, then asked Mr Rabbitte what he got from the lobbyist Frank Dunlop and Mr Brennan said across the chamber: "I got nothing from Michael O'Leary and I'm making that clear. I hope you're not claiming that I did."
Later the Minister for Communications repeated that an allegation had been made by Mr Rabbitte and demanded that he "stand it up and be a man or else withdraw it".
Mr Rabbitte, who raised the issue again yesterday, said Mr Brennan suggested that "powerful forces" were trying to block the break-up of Aer Rianta. The Labour leader asked: "What powerful forces caused the break-up of Aer Rianta in the first place."
He asked why the Government was proceeding with the break-up of Aer Rianta against the advice of the consultants commissioned by the Minister for Transport.
He asked if there was a business plan, if the Taoiseach was in favour of giving Cork and Shannon autonomy within the Aer Rianta structure or stand-alone status and if the issue would go to the High Court.
Mr Ahern said there were ongoing meetings with the trade unions and all the issues had to be resolved, but he stressed that all the "interested groups in the regions have stated that they want autonomy for Cork and Shannon airports".
