Weir, who now lives in Nigeria, told The Sunday Business Post last week that Breen was present when meetings with loyalist paramilitaries took place and that collusion with loyalists was "laughed and joked about".

"Breen had connections with loyalism when I knew him," said Weir. "Breen knew of his cops running around with loyalists. He took no action.

"He was there when submachine guns were handed over to loyalists - it was the done thing at the time. He was only one of many, many people who knew about it."

The loyalist gang of which Weir was a member - and which, he says, Breen approved of - is believed to be responsible for the Dublin and Monaghan bombings, as well as a string of other murders north of the border, including the 1975 Miami Showband massacre.

If Weir's claims are true, it points to further evidence of British state collusion in the worst single atrocity of the Troubles.

An independent panel of international jurors last week found "strong and credible" evidence of RUC and British Army collusion in 24 out of 25 murder cases it investigated, involving the deaths of 76 people.

Weir claims that Brian Fitzsimmons, who was head of the Special Branch in the early 1970s and was based in Newry, Co Down, was aware of the extent of RUC collusion but did nothing to curb it.

Fitzsimmons was killed in the 1994 Chinook helicopter crash off the Mull of Kintyre, which also claimed the lives of 24 other senior British security figures.

Weir denied media reports in recent weeks which stated that he had been questioned by Paddy McEntee SC, one of the country's leading criminal barristers, as part of his investigation into the Garda's handling of the Dublin and Monaghan bombings.

It is understood that McEntee declined to interview Weir in Ireland earlier this year, because it was felt that Weir's evidence was outside the remit of his investigation.

"One needs to understand the other's perspective in history. It's important in terms of the negotiations to get Sinn Fein to sign onto policing that you recognise history.

"You also have to recognise that there are some within the nationalist and republican community who will be sceptical and will want to make sure every i is dotted and every t is crossed before they will agree to the new policing system.

"I have long believed it is in the interests of Northern Ireland and the British government to come forward and come clean.

"Sometimes acknowledging truth is the most powerful way to acknowledge change. What we need is a change in the way the police force operates - that is beginning to happen here.

"We are at a historical juncture. I think it would go a long way for the British government to recognise that acknowledging the atrocities of the past is a way to deliver change for a positive future."

On Monday a report by an international panel of human rights experts claimed it had uncovered considerable and credible evidence of British army and police collusion in 74 sectarian murders in Northern Ireland during the 1970s.

The probe of 25 loyalist atrocities, commissioned by the Derry-based Pat Finucane Centre, found senior Royal Ulster Constabulary and Ulster Defence Regiment officers were aware and in some cases approved of collusion.

It also said officials in London had enough information about collusion to intervene.

On Tuesday the families of six men gunned down by loyalists in a bar in Loughinisland, County Down in June 1994 as they watched a World Cup match, went to Westminster to raise awareness among MPs about allegations of security force collusion in the atrocity.

The Loughinsiland families have announced plans to take their campaign to the European Parliament in Brussels later this month.

Congressman Meehan, a Democrat from Massachusetts, would not be drawn on suggestions that a Truth and Reconciliation Commission in Northern Ireland could enable the British government to admit there was collusion.

He told PA: "I would be satisfied just to have an acknowledgement in many instances and investigations which have integrity and are competent so that these atrocities have their proper place in history."

They also urged the authorities in the Irish Republic to investigate the claims made about their police.

In response to the report, Chief Constable Sir Hugh Orde said the PSNI's Historical Enquiries Team was set up to examine all of the 3,268 killings during the Troubles.

"This particular panel did not meet with or consult directly with the Historical Enquiries Team," Sir Hugh said.

"I would invite them to come and see for themselves how the investigations and work with the families are progressing.''

The report said: "Credible evidence indicates that superiors of violent, extremist officers and agents, at least within the RUC, were aware of their sectarian crimes, yet failed to act to prevent, investigate or punish them.

"On the contrary, they allegedly made statements that appeared to condone participation in these crimes."

The panel was convened two years ago at the request of the Londonderry-based Pat Finucane Centre.

It examined 25 incidents on both sides of the Irish border, including:

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The murder of 33 people in UVF bomb attacks in Dublin and Monaghan on 17 May 1974

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The shooting of three members of the Miami Showband - Fran O'Toole, 29, Anthony Geraghty, 23, and Brian McCoy, 33, after a UVF gang posing as an Ulster Defence Regiment patrol flagged their bus down on 31 July 1975.

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The killing of Patrick Connolly, 23, on 4 October 1972 in a grenade attack on his Portadown home by the Ulster Volunteer Force

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The double murder by the UVF of Catholic Patrick Molloy, 46, and Protestant Jack Wylie, 49, in a bomb attack at Augenlig in County Armagh

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The shooting dead of six men in separate UVF gun attacks on two families in County Armagh on 4 January 1976

The panel added: "As early as 1973, senior officials of the United Kingdom were put on notice of the danger - and indeed some of the facts - of sectarian violence by UDR soldiers using stolen UDR weapons and ammunition, and supported by UDR training and information.

"At least by 1975, senior officials were also informed that some RUC police officers were 'very close' to extremist paramilitaries."

The report also said there had been "allegations by at least one former RUC man that the Gardai, the police force of the Republic of Ireland, was not co-operative in bringing fugitives who fled across the border to justice".

The British government told the panel it would be inappropriate to comment as the murders are the subject of inquiries by a number of agencies.

These included the European Court of Human Rights, the PSNI Historical Enquiries Team, and the Police Ombudsman.

'Final chance'

Copies of the 108-page report have been given to the British government and the Police Ombudsman's Office.

The independent panel who produced the report were: Professor Douglass Cassel of Notre Dame Law School in the US; Susie Kemp, an international lawyer based in The Hague; Piers Pigou - an investigator for the South African Truth and Reconciliation Commission and Stephen Sawyer of Northwestern University School of Law.

Last year, the Irish government said it was giving Tony Blair a final chance to aid an inquiry into the Dublin and Monaghan bombings.

Irish premier Bertie Ahern said he may take a case to the European Court of Human Rights if Mr Blair did not hand over British government files on the bombings.

No-one was convicted of the bombings.