The High Court has ruled that businessman Denis O'Brien should pay all the costs of his failed action over statements made by two TDs in the Dáil about his banking affairs.

Mr O'Brien took his case against the Clerk of the Dáil and the State over comments made by Social Democrats TD Catherine Murphy and Sinn Féin's Pearse Doherty in the Dáil in 2015.

He wanted the court to reprimand the TDs and he claimed they had interfered with a court case he was taking against RTÉ.

In March, Ms Justice Úna Ní Raifeartaigh dismissed Mr O'Brien's case, ruling that the Constitution did not allow the court to intervene in relation to comments made in the Dáil.

She found that what he sought was very far-reaching and could have a chilling effect on parliamentary speech into the future.

Mr O'Brien's lawyers had said he wanted the Dáil and State to pay a portion of the costs of the action because of the novelty of the issues involved.

This morning, the judge ruled that the facts of the case were unusual and had some degree of novelty as well as being of some public importance.

She said there had never before been a case taken in relation to TDs deliberately revealing confidential information, which was subject to a court order.

But she ruled there was "an insufficient degree of novelty" to cause her to depart from the normal rule where the losing party pays the costs of a case.

O'Brien's means not taken into account in decision - judge

Ms Justice Ní Raifeartaigh said she was not prepared to take into account the damage caused to Mr O'Brien in her decision as that would, she said, cause her to criticise Oireachtas members indirectly, something she had declined to do in her judgment.

She said the damage inflicted on former Rehab Chief Executive Angela Kerins as a result of proceedings at a Dáil committee was of a greater degree and distinguished that case from Mr O'Brien's.

Ms Kerins was awarded most of her costs of her failed action against the Dáil's Public Accounts Committee.

Ms Justice Ní Raifeartaigh also said she was not taking into account Mr O'Brien's means in her decision.

She ordered Mr O'Brien to pay the costs of the Dáil and State as well as his own.

The costs of the seven-day case are estimated at around €1m.