The High Court has heard that citizens have no legal remedy whatsoever for anything said about them in the Houses of the Oireachtas, no matter how serious or damaging they believe it is.

Lawyers for the State continued their submissions to the court in the case being taken by businessman Denis O'Brien over statements made by two TDs in the Dáil last year.

Mr O'Brien wants the court to rebuke Social Democrat's TD Catherine Murphy and Sinn Féin's Pearse Doherty over the comments they made about his banking affairs in May and June 2015.

He has also taken the action against the Dáil Committee on Procedure and Privileges over the way it dealt with his complaints. 

Senior Counsel Maurice Collins said it was a tribute to Mr O'Brien's self regard that he thought the statements by the two TDs amounted to a "constitutional coup-d'etat". 

Mr Collins said the Constitution intentionally provided a zone of immunity and a closed universe around "utterances" in the Dáil and Seanad. He said this prevented them being scrutinised by the courts.

Mr Collins said this created an absolute barrier to Mr O'Brien's case.

He was asked by Ms Justice Úna Ní Raifeartaigh if citizens who complain to the Dáil Committee on Procedure and Privileges have a right to have their complaints decided in accordance with fair procedures. 

He said there was no such right as Article 15.13 of the Constitution created an absolute barrier to this litigation.

He said the Committee policed compliance with standing orders regulating business in the Oireachtas.

Mr Collins said if the courts could scrutinise the procedures of the committee, that would involve the court deciding whether it was fair for TDs to make certain statements. He said that was not permissible under the Constitution.

Mr Collins said if Mr O'Brien's arguments were correct, the Oireachtas could be sued for damages and injunctions could be sought against TDs and the House for statements made in the Dáil.

He said Mr O'Brien's case was a carefully constructed effort to try to slip under the radar of the Constitutional provisions.

Even if the Oireachtas brought in legislation tomorrow for some form of tribunal to which citizens could complain about Oireachtas statements, that would breach Article 15 of the Constitution, he said.

Mr O'Brien's lawyers began their reply to the defendants this afternoon.

Senior Counsel, Eileen Barrington, said Mr O'Brien's overarching case concerned the equilibrium provided for in the Constitution between the courts and the parliament.

She said the State was failing to recognise the court's role in maintaining the balance between the separation of powers.

Ms Barrington said the test for court intervention was not whether the "outcome" of Mr O'Brien's case against RTÉ was decided by the statements made by the two TDs in the Dáil but whether they affected the "power to decide" the case or an aspect of it. 

Because the statements did have that effect, Article 34 - dealing with the powers of the courts -  was engaged, she argued. 

The utterances of the TDs effectively decided the substantive dispute between Mr O'Brien and RTÉ and not just his application for an injunction restraining it from publishing details of his private banking affairs.

The case will continue tomorrow.  Ms Justice Raifeartaigh is likely to reserve her decision and deliver it at a later date.