Businessman Denis O’Brien wants the courts to “clearly demarcate” the powers of the Oireachtas and courts in his “unique” action over Dáil statements by two TDs about his banking affairs, the High Court has heard.

The case is “unique in the history of the State” because no one has previously sued alleging statements by TDs in the Dáil effectively decided the outcome of court proceedings, said Michael Cush SC, for Mr O’Brien.

Those statements showed “clear disregard” for the separation of powers between the legislature, executive and judiciary guaranteed by the Constitution, and Mr O’Brien wanted the court to decide “where the boundary lies”.

He said Social Democrats TD Catherine Murphy was “reckless at minimum” in what she had said, and both she and Sinn Féin’s Pearse Doherty trespassed on the judicial domain in their Dáil statements.

That was not remedied by the Oireachtas itself and, when faced with this case, the State argued the courts could not intervene due to the separation of powers, counsel said. The courts could, and should, intervene.

Mr Cush was opening Mr O’Brien’s action against the Dáil Committee on Procedure and Privileges (CPP) and the State over statements made in May and June 2015 by Ms Murphy and Mr Doherty about his banking affairs with Irish Bank Resolution Corporation (IBRC).

The businessman wants the court to declare those statements substantially determined his case aimed at preventing RTÉ publishing that information, breached his rights and constituted “unwarranted interference” with the judicial domain.

He also wants declarations the CPP’s rejection of his complaints about the TDs’ statements was based on an incorrect interpretation of Dáil standing orders and breached his rights to fair procedures.

The defendants deny Mr O’Brien is entitled to the declarations, and plead the court is not entitled to intervene.

The action, before Ms Justice Una Ní Raifeartaigh, is listed to last seven days. Mr O’Brien, the sole witness, will begin evidence on Thursday, the judge heard.

Injunction

Tweets and statements by the TD showed “clear disregard” for the court proceedings, Mr Cush said.

Ms Murphy was clearly “fully conscious” of the injunction but “reckless at minimum” about the effect of what she had to say.

Her primary concern was not for the legislative process but about the extent of the injunction and what it meant for “freedom of the press”, and she wanted to ensure “this got out as fast and as wide as possible”.

He said Mr O’Brien made similar complaints over the Dáil statements by Mr Doherty relating to the businessman’s banking relationship with IBRC.

Following formal complaints by Mr O’Brien, the CPP later decided neither TD had breached the standing orders governing debates in the Oireachtas in their remarks.

Privilege

Mr Cush disputed the defendants’ arguments that article 15.10 (providing each House makes its own rules) and articles 15.12 and 15.13 (providing utterances in the Oireachtas are privileged and members are not “amenable” to any court for such utterances) means the courts cannot intervene.

The privilege in article 15.12 applies only to published utterances, he argued. While the defence insisted article 15.13 means, whatever is said in parliament, the courts can “do nothing about it”, that argument involved using the separation of powers “to undermine the separation of powers”.

There was a “separate” debate about what being “amenable” to a court means, counsel said. Mr O’Brien was not trying to make the TDs amenable to the court and had not joined them to the case. His action was about getting declarations, not damages, and article 15.13 did not prevent the court dealing with this matter.

The case continues.