Denis O’Brien is a “very wealthy” man who should not get any of the estimated €1million costs of his failed case against the Dáil and State, the High Court has been urged.

A person seeking to have a “chilling effect” on parliamentary speech should not get their costs, Sara Moorhead SC, for the Dáil, argued.

She and counsel for the State disputed Mr O’Brien’s claim they should pay “a portion” of his costs for reasons including this was a constitutional case of importance and “particular novelty” brought in the interests of other citizens as well as of Mr O’Brien.

Ms Justice Una Ni Raifeartaigh said she will give her costs ruling on a later date.

Mr O’Brien’s seven day case was against the clerk of the Dáil, the Dáil Committee on Procedures and Privileges and the State.

It arose from statements made on separate dates in summer 2015 by Social Democrats TD Catherine Murphy and Sinn Féin TD Pearse Doherty after Mr O’Brien had got court injunctions restraining RTÉ publicising that information.

In her judgment last week dismissing his case, the judge held what Mr O’Brien sought was “very-far-reaching”, prohibited by the separation of powers under the Constitution and would have a “chilling effect” on parliamentary speech into the future. She upheld the core defence argument Article 15 of the Constitution immunises Dáil “utterances” from suit or scrutiny by courts or tribunals.

When the matter returned to the judge on Friday, Michael Cush SC, for Mr O’Brien, argued several factors, including the importance and “undoubted novelty” of the case, entitled the businessman to “a portion” of his costs against one or other of the defendants.

There was no previous case where a citizen with a court order complained what was said in the Dáil rendered that order pointless, Mr Cush said.

This case had implications beyond its own factual situation and a “particularly novel” feature was that TDs released material subject of a court injunction.

The court itself noted the case raised important issues and its judgment clarified an area of possible ambiguity concerning application of Article 15, he said. The court had also accepted what the TDs did damaged Mr O’Brien and had drawn attention to possible ambiguities in the relevant Dáil standing order.

Mr O’Brien was making a case for every citizen who may have a court injunction and wanted to keep private matters governed by that injunction and, while there was a personal interest, the case meant no personal advantage to Mr O’Brien who had not sought damages, he said.

Counsel also relied on the High Court decision awarding former Rehab CEO Angela Kerins two thirds of her failed action over the conduct of hearings by the Dáil Public Accounts Committee concerning payments to Rehab.

Ms Moorhead, for the Dáil side, said it was clear from many previous cases the Constitution confers immunity from suit on what is said in the Dáil and Mr O’Brien’s case neither raised nor decided anything new. The arguments for Mr O’Brien were “clever and novel” but the law was clear.

It was “extraordinary” to say Mr O’Brien did not take it out of personal interest, it was entirely clear he took it because he was very significantly enraged at the TDs actions, she said. He had also alleged to media outlets the TDs were in breach of the court order but it was established the TDs were not in breach.

While accepting the case was of general public importance, there was no novelty and it was very different from Ms Kerins’ case.

Maurice Collins SC, for the State, said there was nothing novel in the case and Mr O’Brien sued out of personal interest with the aim of having the court “rebuke” and punish the TDs.

The case did raise very important issues because, had Mr O’Brien won, the consequences for parliamentary speech would have been “dramatic and very, very negative”.

Many people are unhappy about what is said in the Dáil about them but very few have the resources of Mr O’Brien, he said.

Mr O’Brien took the case as he was entitled to, must have had advice he was very unlikely to win but he persisted and the court held the Constitution provided an “absolute bar” to this type of action.