The conflict in Northern Ireland was needlessly intensified and prolonged by the "disastrous" activities of a core of army and police officers who colluded with the terrorists responsible for dozens of murders, Britain's top policeman has concluded after a four-year investigation.
Sir John Stevens will today tell the Northern Ireland chief constable, Hugh Orde, that unprincipled collusion "ratcheted up the hatred and bitterness" between Catholics and Protestants, and that the system of recruiting and handling the agents responsible for the killings was "out of control".
His interim report on the inquiry which began by focusing on the 1989 murder of the Belfast solicitor Pat Finucane is expected to criticise the army's covert Force Research Unit.
An FRU agent, Brian Nelson, infiltrated and effectively ran the Ulster Defence Association, a loyalist terror group.
Sir John's team believes that Nelson, who died last week, was responsible for at least 30 murders, and that many of the victims he helped to identify were not involved in terrorism.
"This was absolutely appalling. It was completely out of control," a source close to Sir John said. "If you believe in the rule of law, how can you excuse what was going on? We have to ensure that this never happens again."
One of Sir John's key recommendations is likely to be the establishment of an independent intelligence oversight panel to review the records of all agents recruited by the Northern Ireland police service, the army and MI5.
"There has to be regard for the rule of law, otherwise we will descend into absolute chaos," he source said. "A lot of innocent people were killed."
One of them was Finucane, the report will say.
"If you get into the business of state sanctioned assassinations, you are [morally] dead," said a well-placed source.
"These individuals got into the centre of a loyalist paramilitary killing machine... you cannot justify it. Sir John believes there must be proper central control and proper standards so we never have this nonsense going on ever again."
The inquiry has further avenues to explore before the investigation is complete. A former Northern Ireland chief constable, Sir Hugh Annesley, is expected to be asked whether senior officers police withheld information from the inquiry.
An army double-agent codenamed Stakeknife, who infiltrated the provisional IRA, is also under investigation and will be questioned.
Concern about the behaviour of the security forces and the length of time the investigation has taken has prompted Sir John to publish the interim report.
Many of his recommendations will focus on the structure and role of the Special Branch, the department which was supposed to have overall control of agents in Northern Ireland in the 80s and 90s.
Sir John's team found that there was no overall executive control, and that there seemed to be no proper system or procedure to make officers accountable for what they were doing. Rather than working together, the different agencies were competing with each other.
The reality was brought home when the inquiry's officers arrested more than 100 people and found that the majority of them were agents of or informers for either the police or the army.
Sir John believes that he has debunked the claim by Brigadier Gordon Kerr, who ran the FRU at the time of Finucane's murder, that Nelson saved more than 200 lives while he was operating in Northern Ireland. His team has found evidence he saved two: one of them was Gerry Adams.
Finucane was killed by loyalist terrorists guided to him by Nelson. Sir John's detectives uncovered evidence that some police officers wanted Finucane killed and that the force had been warned he was a target: at least two of the loyalists involved were police informers. But nothing was done to stop the murder.
Sir John believes that his shooting in February 1989 should have been prevented, and that his killers should be brought to justice.
Forty files on 23 soldiers and police officers have been sent to the director of public prosecutions in Northern Ireland, but charges are likely to be brought against a much smaller number.
Because the judicial process is still live Sir John will publish fewer than 20 pages of his report, and he is not expected to give away any details that might jeopardise the chances of charges being brought.
He will give Mr Order a separate report running to several thousand pages.
This has raised the fear that he will never publish a full account of what he has found.
His inquiry, which has cost an estimated £4m, has been repeatedly criticised by the Finucane family, who think it is designed to cover up the truth and delay the public inquiry they want held.