The Taoiseach has said his challenge to aspects of the Mahon tribunal's inquiries into his financial affairs is one of "significant constitutional importance" and one that he is obliged to take in order to uphold the Constitution.
Mr Ahern was granted permission in the High Court yesterday to take judicial review proceedings against the tribunal on three grounds, including a claim that the tribunal has no right to question him about statements he made in the Dáil.
The Taoiseach said today he had "clear legal advice" that it would not be correct for him to answer questions before the Mahon tribunal on statements he had made in the House but he had "no problem" answering questions about statements made outside it.
The Taoiseach said he had been advised by "legal eminent people" that no court or tribunal could challenge a member of the Dáil or Seanad in respect of his or her utterances in the Houses of the Oireachtas.
There were "clear precedents" such as a case taken by Labour TD Brendan Howlin in respect of protecting Dáil privilege, he said.
Mr Ahern said the matter was one of "significant constitutional importance" and that he will seek to uphold the status of parliamentary privilege which has existed since the foundation of the State.
There was "arguably a greater duty on the Taoiseach as head of the Government" to ensure the Constitution is complied with, Mr Ahern said.
Almost everything he had said in relation to his financial affairs in the Dáil had been repeated outside, Mr Ahern said.
The Taoiseach was answering a question from Fine Gael leader Enda Kenny, who said it was obvious that the claim lodged in the High Court yesterday was already in preparation for some considerable time when the Dáil debated a recent motion of confidence in the tribunal.
Mr Ahern said he had supported the Government's amended motion of confidence in the tribunal. His decision to seek a judicial review, he said, was because he had clear legal advice that "it would not be correct" for him to answer questions on statements he had made in the Dáil.
It would be "totally inappropriate", he said.
"Everything I've said in the Dáil has been repeated outside it. I've no problem with anything I've said in the Dáil."
Mr Ahern said it was "nonsense" to suggest he was trying to "conceal or hide" something.
"I stand over everything that I've said in this House."
Mr Ahern is due to resume giving evidence to the tribunal on Thursday next week. He said yesterday he was still going to "totally co-operate" with the tribunal.
After the hearing yesterday Mr Ahern said the case concerned "a few technical legal issues where my legal team advised that I had absolutely no alternative".
Taoiseach Bertie Ahern
As well as the matter of Dáil privilege, the other two issues were "related to professional advice that my legal team got independently, and the tribunal is seeking that advice, and the legal team is saying that that is not proper procedure," Mr Ahern said.
"The third point is where the tribunal has independent legal financial advice, and they won't give it to my people, and my [representatives] are challenging that."
The Opposition are expected to attack the Taoiseach during leaders' questions in the Dáil this afternoon.
Fine Gael leader Enda Kenny criticised Mr Ahern's stance, saying: "What is the Taoiseach hiding? What has he said in the Dáil that he cannot now stand over and defend at the Mahon tribunal?
"The Taoiseach cannot claim to be co-operating with the tribunal when he is trying to dictate to it what questions it can ask him," Mr Kenny said.
Speaking on RTÉ's News at One, Mr Kenny said the court action would have the effect of delaying the tribunal, so increasing its cost.
He questioned whether Mr Ahern had told his Cabinet colleagues about the proposed court challenge when they recently debated an amendment on a Fine Gael motion of confidence in the Mahon tribunal.
Labour leader Eamon Gilmore accused Mr Ahern of "resorting to the High Court in an attempt to prevent a tribunal established by the Oireachtas from questioning him on matters of serious public importance." He claimed Mr Ahern's actions could hold up the tribunal's work for at least six months.
Green Party Senator Dan Boyle said this morning his party's support for the tribunal was "very strong". Mr Ahern's action was a private matter that was not being taken by the Government, he said.
Yesterday, Mr Ahern rejected the contention that he had something to hide. "That's not the case. Anything that I have said, most of the questions that I have been asked are issues that I have said [to reporters] in doorstep [interviews] or that I have said in the [Bryan] Dobson interviews [on RTÉ in September 2006]. I have said all these things outside so . . . I don't think there's anything I have said in the Dáil that I haven't said outside."
He continued that he had no difficulty with what he said in the Dáil being challenged. "It's the Dáil privilege issue that you can't be subject to question outside the Dáil. My legal team would want to go far more and have always wanted to go far more, but I have said I was always willing to co-operate."
The tribunal was not represented in the High Court and is expected to give its first response when the matter comes up for mention on Thursday.