Updated 12:05

The Supreme Court has begun hearing an appeal against the dismissal of Denis O’Brien’s legal action over statements made in the Dáil under privilege.

It’s been just over a year since the High Court refused to intervene in a case that arose from statements made by two TDs, Catherine Murphy and Pearse Doherty, under privilege in 2015.

By revealing details about his private business dealings with the IBRC - details which were protected by court order at the time, he claimed they abused their powers of privilege.

He didn't sue them but asked the High Court to reprimand them.

Dáil speech is protected by privilege but he took legal action over what he claimed was an unfair interference with the work of the courts.

An injunction preventing RTÉ from revealing the same private banking details was in place at the same time.

Mr O'Brien's case raised many issues including the constitutional separation of powers and the courts’ ability to intervene in the work of the Oireachtas.

Ms Justice Una Ní Raifeartaigh ruled against him in March of last year. To intervene would have a chilling effect on parliamentary speech, she said.

Seven Supreme Court judges, including the Chief Justice Frank Clarke, convened this morning for what is expected to be a two-day hearing.

The appeal has so far focused on the court’s decision that it had no say in how the Committee on Procedures and Privileges dealt with his complaint. 

Dáil privilege is considered “absolute” in the Constitution but TDs are restricted by their own parliamentary rules or standing orders.

Standing Order 59 deals with matters that are sub-judice or before the courts and in rejecting Mr O’Brien’s complaint, his barrister Michael Cush has accused the committee of incorrectly interpreting the rule.

A failed application for some of Mr O’Brien’s costs to be paid by the defendants will also form part of his case.

The hearing is due to take two days.