The retired Limerick politician said that there was never any mention of such an allegation at regular cross-border meetings with the Northern Secretary, which were attended by the Garda commissioner and the RUC chief constable.
“If it were a fact it would be seriously embarrassing, but it was never established as a fact,” he said.
He said evidence for such a claim would have been raised “immediately” at the meetings, which he described as “no holds barred”.
The tribunal is investigating claims that a garda leak led to the IRA ambush which killed two senior RUC members, chief superintendent Harry Breen and superintendent Bob Breen on 20 March 1989.
Mr Collins said that a report in the wake of the ambush assistant commissioner Ned O’Dea was sent to Dundalk on a “fact finding mission”.
The O’Dea report concluded there was no leak from Dundalk garda station.
Press reports in the wake of the killings, and the earlier murders of Lord Justice Maurice Gibson and the Hanna family in 1988 had suggested there was an IRA “mole” within the Gardai.
But Mr Collins agreed with Darragh Lehane, representing Mr Owen Corrigan, that there was “a propaganda war”, and it would be in the IRA’s interest to discredit policemen.
“You don’t destroy a good police force, which we are lucky to have, by investigating every time some silly article appears in some tabloid,” he said.
Earlier, the tribunal chairman concluded that a report prepared by a senior garda officer following the abduction of retired detective sergeant Owen Corrigan by the IRA is not covered by legal privilege.
The garda commissioner’s legal team had claimed that the report was privileged, and any evidence relating to it should be heard in closed session.
Michael Fanning, who was one of the first gardai on the scene after the 1995 kidnapping of Mr Owen Corrigan, said that Mr Corrigan “would never put anybody in danger”.
Mr Corrigan has described allegations that he was the source of a leak to the IRA about the movements as a “monstrous lie”.
The judge also said that a confusion over forwarding addresses abroad meant that former assistant commissioner Kevin Carty was not informed he was due to appear at the tribunal to give evidence.
The tribunal has since been in contact with Mr Carty, now based in Vienna working with the United Nations, to arrange a new date for his evidence.
“I accept that he didn’t intend any disrespect to the tribunal,” chairman Peter Smithwick said.