You can understand why the leadership of the IRA is reeling at the claim that the deputy head of its internal security organisation has been a paid informer since 1978. But why should the core of the British state be thrown into panic at the naming of Alfredo Scappaticci as their top agent, codenamed Stakeknife?
The answer is simple. It shows how Britain's role in the 30-year war in Northern Ireland was as much based on lies and brutality as the invasion and occupation of Iraq. Far from keeping two warring sides apart, the British state either allowed or organised the murder of large numbers of mainly Catholic citizens to protect a sectarian set-up. Scappaticci denies he's an informer.
But it is clear 'Stakeknife' was recruited by the most shadowy British intelligence outfit in Northern Ireland, the army's Force Research Unit (FRU), 25 years ago. The Labour government of the time and its Tory predecessor had already cast aside two chances for peace.
The British state turned instead to the methods of a dirty war directed not only at the IRA, but at the base of Republican support in Catholic working class areas.
The late 1970s and early 1980s marked the high point of an assassination policy. Having Stakeknife led the British state, through the FRU, to authorise him to kill possibly dozens of people. Some were Republicans accused by Stakeknife's IRA security squad of being informers and killed on his say-so to protect his identity. Others were fellow agents who the army or MI5 judged had become troublesome or past their use-by date. Many, however, were totally unconnected with 'the Troubles'.
In 1987 no one could make sense of the murder of an elderly Catholic man, Francis Notarantonio, by the Ulster Defence Association (UDA). There were plenty of random murders of Catholics by Loyalist gangs. But Francis's killers held a celebration for executing 'the head of the IRA in Ballymurphy'.
He was, as Republicans and the British army knew, nothing to do with the Provisional IRA. The naming of Scappaticci lends weight to revelations a few years ago about the murder.
Loyalist gunmen originally set out to kill Scappaticci. But the British army forged an intelligence dossier (familiar?) which implicated Francis Notarantonio as a top IRA man and passed it to the Loyalists. British officers decided an innocent man could satisfy Loyalist bloodlust. It was easy to redirect the execution, because the FRU had an agent at the heart of the UDA - Brian Nelson.
Information passed to Loyalists through Nelson was responsible for the murder of 30 Catholics, including Belfast solicitor Pat Finucane. That is according to the handful of pages we have been allowed to see of the investigation into army collusion in Northern Ireland, conducted by Metropolitan police chief Sir John Stevens.
Stevens' interim report last month said, 'The security forces sanctioned killings. Informants and agents were allowed to operate without effective control and to participate in terrorist crimes.' An obscene and astonishing reality is emerging from revelations by former FRU soldiers such as the man known as Martin Ingram.
That is why defence secretary Geoff Hoon has mercilessly tried to impose gagging orders on him. The British army ran agents on both sides. To protect infiltrators in the Republicans, they used infiltrators in the Loyalists to organise the murder of uninvolved Catholics.
This leaves aside the direct murders by the British army and attempts in the 1970s to destabilise the Labour government.
How much of this will ever come out through investigations by senior establishment figures such as Stevens? Not a lot, if the public inquiry into the murder of 13 unarmed Catholics by the paratroop regiment on Bloody Sunday in 1972 is anything to go by. Martin Ingram did eventually get to give evidence on Monday of this week. He cleared Sinn Fein's Martin McGuinness of the smear, spread by an MI5 agent known as 'Infliction', that he fired a shot on the day.
But Irish journalist Eamonn McCann reports: 'MI5 has been allowed, by the tribunal under Lord Saville, to decide what witnesses will be called and what questions will be asked. Earlier this month, the inquiry heard that the witness statement of a key retired MI5 agent-runner called 'Julian' had been drafted for him by serving members of MI5 after they'd consulted documents in the MI5 archive. What documents? Nobody knows. Nobody was permitted to ask.'
Perhaps a few junior heads might roll. But we already know the fate of senior figures who orchestrated the dirty war. The former head of the FRU, brigadier general Gordon Kerr, is now the military attache (ie head of spying) at the British embassy in Beijing - making him a key figure in British intelligence.
According to Irish magazine Phoenix, he has been secretly sent to Iraq. That's the place where we are told Britain will use its experience in Northern Ireland to win hearts and minds and avoid the trigger happy antics of the US Marine Corps.
It's also the place where rather a large number of dodgy documents have turned up over the last month.