The chairman of the Centre for Public Inquiry (CPI) has described allegations made by Minster for Justice Michael McDowell against the CPI executive director Frank Connolly as a "drumhead courtmartial".
Retired High Court judge Mr Justice Feargus Flood, who chairs the CPI, said Mr Connolly had the right to presumed innocence and due process.
He was reacting on RTÉ radio this morning to Mr McDowell's allegation that Mr Connolly had travelled to Colombia four years ago on a false passport.
The Minister admitted yesterday that he leaked the allegedly falsified passport application with Mr Connolly's photograph on it to the Irish Independent.
His actions caused a storm of controversy, with Sinn Féin calling for his resignation, and other political parties and legal commentators saying he was acting dictatorially and had set a dangerous precedent.
This morning an angry Mr Justice Flood told Morning Ireland: "The citizens of this country are innocent until they are proven guilty, in accordance with the rules of law.
"The Minister cannot override the Constitution under any circumstances. The Constitution provides that justice shall be administered in public in court."
Mr Justice Flood referred to sections 38 and 40 of the Constitution, saying: "There is a court service and judges who are trained to administer that service, and I certainly believe that he [Mr McDowell] cannot override that.
"There is only one judiciary and I was a member of it, I am no longer a member of it," he said. "I don't have any capacity to pass judgment on any fellow citizen."
When asked if he had asked Mr Connolly about his alleged republican links, Mr Flood referred to denials Mr Connolly has made.
Mr Justice Flood said he was not entitled to pass judgment on anyone. "I stand four-square behind him [Mr Connolly] until this extent; I stand four-square behind all citizens, absolutely all citizens, however great scoundrels they may be, until they have been processed through due process of law in a proper court and not a drumhead courtmartial."
Mr Justice Flood - who was formerly the chairman of the planning tribunal - said that Mr Connolly's salary of €120,000 - €125,000 per annum has been "wiped out" by Mr McDowell's actions.
"By the end of this year the funds will have been exhausted, the staff will have to be let go, and he will be destitute of any income because of a statement made in privileged circumstances, it cannot be tested.
"If you want to test it then why not go down to the DPP? Ask him what he decides. He's the deciding man, not the Minister," Mr Justice Flood said.
"The officer who decides whether a citizen will be prosecuted is the Director of Public Prosecutions and no one else."
Mr McDowell alleged under Dáil privilege last week that Mr Connolly had travelled to Colombia using a false passport in the company of his brother Niall, who later became one of the Colombia Three; and Pádraig Wilson who has been convicted on IRA-related charges.
Mr Connolly has strenuously denied the claim.
Funding for the CPI from American billionaire Chuck Feeney was withdrawn the day after Mr McDowell made his allegations in a written reply to a question from Independent TD Finian McGrath. The Minister had been lobbying Mr Feeney for some months in relation to Mr Connolly's background.
The CPI was established to inquire into issues it considered to be of public importance. It has produced two reports, including one on the controversial Corrib gas pipeline being built in Co Mayo by a Shell-led consortium.
Mr Connolly believes Mr McDowell has been co-ordinating attacks on him through the Irish Independentand said last week's claim in the Dáil was an attempt to undermine the CPI and was developed by "those seeking to protect vested interests".