Businessman Denis O'Brien has told the High Court that he and his family received threats to their lives at the end of May 2015, at the height of the controversy about the disclosure of his banking details in the Dáil.

Mr O'Brien was giving evidence in his case against the Dáil and the State over statements made by TDs Catherine Murphy and Pearse Doherty about his banking affairs in the Dáil in May and June 2015.

He said he had often received nasty comments but never anything of this nature before and the death threats were probably the most serious and he reported them to gardaí.

He agreed the threats were made at the same time as the events at the centre of this court case.

But he also agreed that he was not suggesting that either of the two deputies had been responsible for the threats.

He said he could not pinpoint what had made these people make these threats.

Mr O'Brien's lawyers say the comments of the two deputies in the Dáil effectively determined the court case he was taking at the time against RTÉ to stop a report about his banking affairs from being broadcast.

Mr O'Brien told the court that it would be pretty extraordinary if you had a situation where every citizen was subject to having all their banking details disclosed and their privacy invaded.

He said his lawyers had sought a court order against RTÉ which was granted.

Meanwhile, two miles down the road, in the Oireachtas, information which was part of that order was being revealed.

He said this meant no one would have any protection from any court order because it could be broken by members of the Oireachtas.

He said this would be a very bad thing for the country's reputation internationally.

Mr O'Brien said that if someone's personal banking files were stolen as they were, in this case, and given to a member of the Oireachtas, then the member of the Oireachtas should go to the guards instead of reading the information out in the Dáil.

He said he was in court today to see if there was a way that this would never happen again to any citizen.

He said Ms Murphy and Mr Doherty "totally knew" what they were doing when they made the statements they did.

Under cross-examination, Mr O'Brien was asked what remedies he wanted from the court.

He agreed one remedy would be that the Ceann Comhairle could be more proactive about preventing TDs from naming people in such a situation.

He also agreed he would like the court to put down some sort of guidance about how debates should be conducted.

Mr O'Brien agreed with senior counsel for the Dáil Committee on Procedure and Privileges, Michael Collins, that he wanted the High Court to censure or rebuke the Dáil deputies as a whole and the committee for the utterances of the two TDs on the floor of the House.

He also agreed that he wanted the court to express disapproval of what the two TDs did and the way the committee dealt with it.

And he agreed that he wanted one branch of government, the judiciary, to deplore what had occurred and to make adverse comment and adverse declarations about the statements made on the floor of the House.

Mr Collins asked Mr O'Brien if he wanted all Dáil deputies to learn a lesson and not behave in this way in the future.

Mr O'Brien said he wanted them to respect the High Court.

He said if a citizen had a High Court injunction Dáil deputies should not interfere with it and they should be responsible. He agreed he wanted the court to lay down a line beyond which Dáil deputies should not go.

Lawyers for the Dáil Committee on Procedure and Privileges, said the High Court had no power to intervene in the process of freedom of speech of Dáil deputies on the floor of the House.

Mr Collins said Article 15.13 of the Constitution expressly prevented the courts from interfering in what members of the Oireachtas say on the floors of either house.

He said the circumstances of this case were not so exceptional as to allow the court to cross the line between the judiciary and another branch of government.

He said the TDs' had not "determined" Mr O'Brien's case against RTÉ as the exercise of free speech by Dáil deputies could never amount to the exercise of a judicial function.

Mr Colllins said the court did not have the power to intervene in the internal workings of a Dáil committee.

The committee did not make Mr O'Brien subject to its processes and was not seeking to infringe on his rights.

It was conducting an internal inquiry into its own affairs and Mr O'Brien had no right to have the inquiry "done properly".

Mr Collins said the idea that deputies would be free to say what they want on the floor of the house was a critical and integral part of the separation of powers.

He said any of the remedies sought by Mr O'Brien required the High Court to examine statements made by Dáil deputies and their effect on Mr O'Brien and this was something the court could not do.

Earlier Mr O'Brien said in his mind what the two deputies had done in the Dáil was a flagrant breach of the High Court injunction in his case against RTÉ.

He said it had never happened before and the two TDs knew exactly what they were doing, adding that it was very well thought out and one of the deputies was tweeting at the same time as they spoke.

Mr O'Brien agreed that his lawyers had written to two or three media outlets threatening legal proceedings if they reported on what Ms Murphy said in the Dáil.

Mr O'Brien said he did not feel the Committee on Procedure and Privileges had behaved particularly well.

He said they had not upheld his complaints and had leaked their decision to the Irish Times four days before they wrote to his lawyers and said he felt they did not investigate the issue properly.

Mr O'Brien said he was "nearly blinded" with law but he looked at it very simplistically and wanted to know that if a citizen was given an order by the High Court it would be watertight.

Mr O'Brien's lawyers had argued that Deputies Murphy and Doherty were interfering with an ongoing court case.

Mr O'Brien agreed with counsel for the State Maurice Collins that if he was successful in this action, the mere fact of issuing High Court proceedings would "greatly restrict" Dáil speech.

He accused Mr Collins of trying to make victims of the two TDs saying he was the one who had been wronged.

His banking details had been stolen, given to Dáil deputies and revealed in the middle of a court process, and hopefully if he was successful in court, this would never happen again, he said.

Mr O'Brien added that he would hope people's privacy would be respected and people's private banking matters would not be ventilated in the Dáil. It could be medical records next, he said.

He said it was "unlikely" he would personally sue Ms Murphy and Mr Doherty if he was successful in this case.

Death threats outlined

In his witness statement to the court, Mr O'Brien said that on 31 May 2015, he had received an email from a person who expressed the desire that he and his family would die in their sleep.

He said the email also contained a "chilling fantasy" that the sender had about slitting Mr O'Brien's throat.

He said on the same date, an individual, who said he was a former member of the French Foreign Legion, referred to a photograph of Mr O'Brien and posted a comment on Facebook saying "I'm pretty good with a sniper rifle and this ****'s got a big head" and also made reference to military grade ammunition.

Mr O'Brien said he had been the subject of media, public and political comment involving regular criticism both generally and for his attempts to protect his privacy and this was something he had learned to accept.

He said he regularly received nasty, hateful emails, but he had never been the subject of anything approaching the level of this.

He said he was fearful for himself and his family and reported the threats to An Garda Síochána on 5 June 2015.

Mr O'Brien also said it was important that orders of the court were obeyed and not undone by a political process.

He said deputies Murphy and Doherty had interfered with his ability to secure an order from the court and then undermined the order.

He said if it was permissible as a matter of Irish law for individual deputies to behave in that manner, he believed that had profound implications for the country as a whole and all its citizens.

He said in bringing these proceedings he hoped to establish that that was not so.

He said he was not seeking damages, but believed it was vitally important to establish what is permissible and what was not.