Army records also show that in 1987 the agent-running arm of military intelligence called the “Force Research Unit” (FRU) recruited a member of the UDA to help ensure “the proper targeting of Provisional IRA members . . . prior to any shooting”. The agent, Brian Nelson, was paid nearly £50,000 by the FRU, which arranged for him to be set up as a mini-cab driver. This gave him cover to enter hard-line republican areas to help identify IRA targets. The FRU operated “almost as if it was a maverick unit”, says Sir Hugh Orde, the former Chief Constable of the Police Service of Northern Ireland (PSNI).

Eventually, the FRU reported that thanks to Nelson, UDA targeting had become “more professional”. Rarely was that so: more uninvolved Catholics were killed than IRA members, despite Nelson claiming to only want “to attack legitimate targets.”

Nelson was also involved in targeting the Belfast solicitor Pat Finucane, who represented several high-profile IRA clients. Finucane had bullet after bullet fired into his head and neck at a distance of 18 inches after two masked gunmen burst into the kitchen as the Finucane family sat down to supper in February 1989. “It’s not a place I care to go,” says Finucane’s eldest son Michael, who witnessed the murder together with his mother, younger brother and sister. At least one Special Branch officer appears to have known Finucane was being targeted, as did MI5, who had effectively helped to set him up as a target by using one of their agents in the UDA to profile him as an “IRA solicitor” in a loyalist magazine.

Between them, the FRU, MI5 and the Special Branch ran scores of agents. Most, though, were run by the Branch, which has most questions to answer in Northern Ireland’s “dirty    war”.

Many lives were unquestionably saved by the Branch. But you don’t get actionable life-saving intelligence from milkmaids. That came mostly from agents deep within the terrorist organisation who often had to prove their loyalty to those organisations by participating in terrorism, even murder. This was the central dilemma for all three intelligence agencies: to what extent should the state turn a blind eye to crimes committed by its paid agents for the greater good? An agent “can’t sort of say ‘Oh, hang on — I don’t do shootings but I will do bombings,’ you know, ‘come back next week and invite me to do one’,” says a former head of the Branch, Ray White. “No, an agent does exactly what he is asked in relation to those matters.”

However, in some cases it is by no means clear that any greater good did actually come from the more collusive relationships between Branch handlers and agents. The former Police Ombudsman for Northern Ireland Nuala O’Loan says “hundreds and hundreds” died because these agents were not brought to justice — a figure disputed by the Police Service of Northern Ireland Chief Constable George Hamilton. Some, however, are alleged to have been serial killers.

One loyalist agent in the UVF in North Belfast, Garry Haggarty, is now facing no fewer than 212 charges, including five murders, six attempted murders and 31 conspiracies to murder with a further 300 offences to be taken into consideration. Some Branch officers are said to have indulged this level of criminality for a decade.

Several CID officers have told me the Branch often obstructed their investigations into killings in which agents were involved.

In my view, however, attempts by Sinn Féin and others to portray the loyalists as “state-sponsored” forces systematically protected by a sectarian police force don’t actually stack up. For a start, the loyalists were remarkably unsuccessful, never managing to kill off the ruling IRA army council. Nor do the large numbers of loyalists prosecuted by the RUC sit easily with this version of history.