Irish financier Phil Flynn has challenged Ulster Unionist peer Lord Laird to repeat allegations about him outside parliament.
Lord Laird used the legal protection of parliamentary privilege on Tuesday to raise questions about the relationship between Mr Flynn, a former vice-president of Sinn Fein, and the Taoiseach, Bertie Ahern.
Ulster Unionist peer Lord Laird used parliamentary privilege
Lord Laird called for the police fraud squad to examine any loans made locally by Mr Flynn's former firm, the Bank of Scotland (Ireland).
In February, Mr Flynn resigned from his position on the Irish government's decentralisation committee after being interviewed by the Irish Criminal Assets Bureau during an investigation into money laundering.
Speaking in the House of Lords, Lord Laird claimed Phil Flynn "was prosecuted for IRA membership in 1974.
"The police understood that he had been their chief finance officer. He became vice-president of Sinn Fein from 1980 to 1985," he said.
"When, in 1997, Bertie Ahern became Irish prime minister, Flynn had already been his friend, adviser and main troubleshooter for some years."
The peer said that Mr Flynn, who left active politics for a career in trade unionism and business, became a "pillar of Irish society".
However, Lord Laird said: "The Irish police knew different.
"In 2002 and 2003, they observed Brian Keenan, currently an active member of the IRA Army Council, staying for some time at Flynn's home in Dublin.
"They also observed Slab Murphy, the IRA Army Chief of Staff, meeting Flynn on a regular basis. They reported this to the government. Nothing happened."
Referring to the Irish police's investigation into the IRA and money laundering, Lord Laird said: "The police now believe that the IRA have up to £2bn in assets in Dublin: in pubs, hotels, houses and other legitimate investments.
"They are based on a cash deposit of stolen money, and between 80% and 90% of lending by a 'friendly institution'."
Questioning the relationship between Mr Flynn and Taoiseach Bertie Ahern, Lord Laird asked: "Was there a deal to allow the IRA to buy their way into respectability with stolen money?
"What is the link between Sinn Fein and Ahern that allows some in the Irish government to turn a blind eye to the 'state within a state'?"
The peer went on to refer to the Taoiseach's offer, now rescinded, to release the killers of Garda Jerry McCabe as part of any peace deal.
He claimed that "Sinn Fein have undue influence over Fianna Fail through a combination of money and blackmail".
'Cover of privilege'
Phil Flynn was formerly the chairman of the Bank of Scotland (Ireland).
In his speech, Lord Laird called on the Police Service of Northern Ireland's fraud squad to "urgently inspect" the bank's Belfast loan book.
Contacted by the BBC, Mr Flynn said he had not seen Lord Laird's speech but would respond fully if the Ulster Unionist peer repeated his allegations without the cover of parliamentary privilege.
He said that much of what he had seen attributed to Lord Laird previously had been inaccurate.