Mary Lou McDonald says that if it emerges that senior Garda management were prepared to mislead the Garda Commissioner, then it is a major worry for both O’Sullivan and the Minister for Justice.

The deputy Sinn Féin leader told RTÉ's Today with Sean O'Rourke that there was no point trying to side step these issues, "they need to be established,"she said.

Ms McDonald made the comments following the emergence of details of an exchange between Ms O’Sullivan’s senior counsel Colm Smyth and Mr Justice O’Higgins.

According to leaked transcripts of the commission hearings, seen by RTÉ, early in the hearings Mr Smyth had said his “instructions from the commissioner” were “to challenge the integrity . . . of Sgt McCabe”.

However, on the morning Ms O’Sullivan was to give her evidence, Mr Justice O’Higgins sought further clarification and Mr Smyth informed him his “instructions at all times were to challenge the motivation and credibility of Sgt McCabe”.

Mr Smyth said it was an error on his part when he had earlier stated he was instructed to challenge Sgt McCabe’s “integrity”.

“We need to know what instructions did she give and why. These instructions were subsequently changed - why was that?,” Ms McDonald said.

“Decisive action is needed now by the Minister. I hope Government acts quickly. We need to understand the sequence of events, to know exactly what happened. We need to reiterate Maurice McCabe’s good name and standing.

“We need to know the provenance of these documents. There are obviously constraints re lawyer/client privilege but that should not prevent confirmation from the commissioner via the Minister on the position that was taken, the instructions given to legal counsel in respect of Maurice McCabe. These need to be clarified as a matter of urgency.”

Ms McDonald said that a lot of similar controversies have distracted focus from the core findings and recommendations of the report itself. She said that the political focus needs to get back to the report.

“It is legitimate now that these matters are in the public domain that we have clarification. It is important that the commissioner clarifies was that the advice given, why was that advice given, clearly there was a change in tack, why did that happen?

“There is every likelihood that in the first place the commissioner or her office, instructed counsel in that very robust way, to go on the attack against McCabe, on the basis of information her office received.

“That information subsequently changed as a result of the foresight that Sgt McCabe had to record the conversation. What does that tell you about the pressure he was under? Then the advice changes. There is a whole range of information in the system that needs to be accessed.”

Ms McDonald said that the issue goes beyond the O’Higgins report, to the culture within the organisation.

On the same programme Fianna Fáil TD for Meath East, Thomas Byrne said some way must be found to publish the entire transcripts.

“Clearly this is an issue that Frances Fitzgerald didn’t handle well. This needs to be addressed by her and a way has to be found to ensure full confidence in the justice system.”