The High Court has begun hearing business man Denis O’Brien’s legal action against a number of TDs and the Dáil Committee on Procedure and Privileges.

The businessman claims remarks made in the Dáil about his personal banking affairs effectively determined a court case he had initiated against RTÉ.

In opening the case this morning, Michael Cush, acting for Denis O’Brien, said his client contends that the words of Deputies Catherine Murphy and Pearse Doherty in the Dáil had the effect of determining a case that was pending before the courts.

Mr O’Brien said he had already obtained a temporary injunction preventing RTÉ from broadcasting what he considered to be confidential information about his personal banking affairs with the IBRC - but that it was effectively worthless when TDs revealed the details.

Parliamentary debate is protected by absolute privilege - which grants politicians the right to speak without fear of punishment or legal action.

However, Mr. O’Brien contends that the privilege cannot be relied on when the subject matter is before the courts.

His lawyers will argue that to do so is a violation of the separation of powers between the judiciary and the legislature - and he is seeking a declaration to that effect.

This hearing is expected to take up to eight days and will hear from Mr. O’Brien on Thursday.