Mr Tom Gilmartin has accused the Taoiseach, Mr Ahern, of lying to the Mahon tribunal about an alleged meeting in Leinster House.
Mr Gilmartin today repeated his claim that he met the then taoiseach, Mr Charlie Haughey, Mr Ahern and a number of other Fianna Fáil cabinet ministers in Leinster House on February 1 st1989.
He said the meeting was also attended by Mr Padraig Flynn, Mr Seamus Brennan, the late Mr Brian Lenihan, Mr Ray Burke and another man he did not recognise, but thought was Mr Gerard Collins. He also said Mrs Mary O'Rourke came into the room at one stage.
All of those alleged to have been present, with the exception of Mr Haughey and Mrs O'Rourke, have formally denied any knowledge or recollection it took place. The tribunal heard Mr Haughey was unable to direct his legal team "due to ill-health". Mrs O'Rourke has told the tribunal she was briefly present, after being asked to attend by Mr Flynn.
Mr Bernard Madden, SC for Mr Flynn, said his client would say he had no recollection of this meeting. He said Mr Ahern had also said in his statement to the tribunal it was his "firm belief" that he had no recollection of it either.
Asked by counsel if he thought Mr Ahern was lying, Mr Gilmartin replied: "The word recollection seems to be a nice word for getting around the house rules. But he is actually lying."
All the others who say they were not at the meeting were "lying" too, he added. "And Mr Flynn is not telling the truth."
The tribunal chairman, Judge Alan Mahon pointed out that there was a significant difference between Mr Flynn saying he did not recollect the meeting taking place and saying it did not take place at all.
Mr Madden consulted with his client and told the tribunal: "[Mr Flynn] has no recollection of ever attending any such meeting in Leinster House or anywhere else."
Judge Gerald Keys pointed out that just because someone says they have no recollection of a meeting, it doesn't necessarily follow that it didn't take place or that he wasn't there.
Earlier, the tribunal refused an application by a number of legal representatives of parties against whom Mr Gilmartin has made allegations to have his initial statement released to them. They argued there were a number of inconsistencies between this account and his formal statement.
Mr Gilmartin made the first statement to his then solicitor, Mr Noel Smyth, in 1998. He subsequently made a formal statement to tribunal lawyers, which was read out by Mr John Gallagher SC at the beginning of the current module earlier this month.
Judge Mahon, ruled that, as the first statement was submitted by Mr Smyth on the basis of confidentiality, it could not be released. He also noted that in furnishing his preliminary statement, Mr Gilmartin reserved the right to make any amendments or alterations to it before making his final sworn statement to the tribunal.
