Barron spells it out at every turn ? he was unable to reach conclusions about collusion because he was refused access to the necessary intelligence.

Initially, British prime minister, Tony Blair, promised cooperation. Then the NI office simply ignored Barron's requests for information.

Barron persisted. It took over a year for the Secretary of State for NI to write and say there were 68,000 potentially relevant files at the NIO, millions at the Ministry of Defence. In the end a 16-page letter was all that was sent.

Barron repeatedly pointed out he needed to see original documents. However, "no copies of any original documents were forthcoming." The scope of the report, Barron notes, is limited as a result.

It took Sir John Stevens 14 years and three inquiries (with greater powers and resources than Barron's) to conclude earlier this year that there was collusion during the 1980s between loyalists and British security forces. He defined it as "the wilful failure to keep records, the absence of accountability, the withholding of intelligence and evidence, and the extreme of agents being involved in murder." He added that his inquiries had been obstructed. By this definition, Barron has revealed that collusion is still being practised.

There is plenty of other evidence. There's the obstruction of the Saville inquiry, including the destruction of evidence. The refusal to provide documents to a Co Tyrone coroner carrying out inquests into a number of controversial loyalist and security force murders during the 1990s. The British government has also reneged on a commitment to publish the report of Judge Peter Cory.

Stevens described the "cultural" nature of collusion. In the 1970s, that culture was even more rawly apparent. In 1974, hardline unionism was intent upon wrecking the Sunningdale agreement. The Reverend Ian Paisley and David Trimble were on the same side as the loyalist paramilitaries, and were content to let the UDA and the UVF provide the muscle for the Ulster Workers Council "strike".

There was no outcry when a UDA spokesman said he was "happy" about the DublinMonaghan bombs. The UDA was legal, and so, at the time of the bombs, was the UVF. The 'B' specials, a quasi paramilitary element of the police, had become the UDR.

The Barron report reveals a network of loyalists, policemen and soldiers who, from the start of the decade, murdered dozens of people, mostly Catholic civilians. They did so with a remarkable degree of impunity while the authorities, north and south of the border, and in the UK, were preoccupied with the "real" enemy, the IRA. In a recent documentary, Progressive Unionist leader, David Ervine called the Dublin-Monaghan bombs "returning the serve".

One of the most remarkable sections of the report is its final appendix, "information received concerning certain weapons". This is the ballistic history of seven guns and shows "the unbroken chain from gun to gun" through a series of murders and attempted murders in midUlster beginning in 1973.

The chain included, in 1975, three murders at Donnelly's bar in Silverbridge, the murders of two men at a fake UDR checkpoint, the murder of IRA man John Francis Green in the Republic, the murders of members of the Miami showband and the murder of Dorothy Trainor in Portadown. In 1976, they included the murders of three members of the Reavey family, and the attack on the Rock Bar in Tassagh.

One of the guns was found in 1979 on lands belonging to a UDR man who was convicted of UVF membership. Four men were convicted of the Rock Bar attack ? all of them members of the RUC. Several of the UVF men who ambushed the Miami showband, were also in the UDR.

Barron found that it was probable the guns were kept at the farm at Glenanne belonging to James Mitchell, an RUC reservist. This farm was the hub of a group of paramilitaries and members of the security forces. Members of the group, led by a UDR man, carried out the massacres at Dublin and Monaghan. In 1978, Mitchell was convicted of storing arms for the UVF. Barron was told the explosives used in the Dublin Monaghan bombs had also been stored there.

There was a similar farm in Tyrone.

The chain was unbroken because the perpetrators of these attacks weren't caught, or investigations were haphazard, or charges were dropped, or light or suspended sentences were given. The same individuals turn up again and again, but the links weren't noted.

Some of the perpetrators weren't prosecuted despite evidence against them. On 28 October 1973, Robin Jackson murdered Patrick Campbell, a 34-year-old Catholic from Banbridge. He shot him on the doorstep of his home.

Campbell's wife picked Jackson out during a police identity parade. However, a murder charge brought against him was dropped after it was claimed Mrs Campbell knew Jackson ? a claim she denies.

Six months later, the loyalist was one of those who bombed Dublin and Monaghan.

Barron notes that in 1976, the security forces came up with evidence, including Jackson's finger print on one of the guns in the chain above. The judge said it was clear he had touched it, but unclear "as to whether he did that wittingly or unwittingly, willingly or unwillingly." He was released.

In 1977, he was named in court as the gunman who shot William Strathearn in Ahoghill, Co Antrim. Two RUC men, Billy McCaughey and John Weir were convicted.

Jackson wasn't even questioned, for "operational reasons" which have never been detailed.

McCaughey and Weir went on to tell tales about their exploits as policemen and paramilitaries. Colin Wallace and Fred Holroyd, both of whom worked for British intelligence agencies did the same.

All four have grievances, and have been dismissed as sources. Barron reassesses their evidence, concluding that they are to be taken seriously.

All allege collusion.

Barron follows the trails as far as he can. He notes that the British authorities claimed they had interned the perpetrators of the Dublin-Monaghan atrocities, and that charges would be forthcoming. They were not.

Some of the Dublin-Monaghan gang, including Jackson, are dead. Others are alive and well. One of the UVF men closely associated with the bombings, though interned at the time they were carried out, was a leading figure in the Orange Order's dispute at Drumcree in the late 1990s.

Mitchell, the owner of the farm at Glenanne, and now in his 80s, still lives there. This weekend, Willie Frazer, spokesman for Families Acting for Innocent Relatives, defended him as a "well respected man" who "just got caught up".