Political fury hangs over a secret hotel car-park meeting in which a former garda commissioner is accused of attempting to discredit a whistle-blower exposing corruption within the force.

The meeting was between former chairman of the Public Accounts Committee (PAC) John McGuinness and former commissioner Martin Callinan two years ago – but first details only emerged last week.

McGuinness has claimed Callinan attempted to discredit whistleblower Sergeant Maurice McCabe who was due to give evidence to the PAC.

The hidden meeting and the attempt in it by Callinan to discredit McCabe were only made public by McGuinness in the Dail last week.

He told RTE Radio that he didn’t mention it two years ago because he wanted to ensure McCabe gave his evidence before the PAC when efforts were being made to stop him.

Knowledge of the meeting wasn’t available to another inquiry, headed by Justice Kevin O’Higgins last year, which found McCabe acted out of genuine and legitimate concerns and that he showed courage and performed a public service at considerable personal loss.

But the report also stated that there was not “a scintilla of evidence” to substantiate an allegation of corruption against Callinan.

Now Sinn Fein deputy leader Mary Lou McDonald, who was a member of the PAC two years ago, wants Callinan to reply to what McGuinness claims he said.

Callinan retired earlier than expected in 2014 following his description of the actions of two whistleblowers, including McCabe, as “disgusting.” His early retirement also followed another report that there was a widespread breach of policy by those administering the garda system. He was succeeded by the first woman commissioner, Noirin O’Sullivan.

She now faces her biggest crisis after the new independent Policing Authority told her last week of its “deep unease” at the organization and its management culture.

Later this month, O'Sullivan will appear twice before the Policing Authority, which is chaired by former Revenue Commissioners chairwoman Josephine Feehily.

This time, she will be grilled in public as the authority seeks “evidence of a tangible response” to lessons learned.

O’Sullivan said through a spokesman on Monday that she was not aware of any private meeting between Callinan and McGuinness.