Moreover, the kind of collusive relationships that existed between the British state and its informants existed to a much greater extent between the state and its informants in the IRA. The FRU, for example, ran the head of the IRA’s so-called “nutting squad” as an agent. Whilst informing to the British, his IRA role was to identify fellow traitors to the IRA. Some were then tortured into confessing before being executed. To protect this top agent, other lesser agents are said to have been sacrificed. The full truth of this case has yet to emerge but it rather suggests that compared to the agents they were running in the IRA some of the Branch’s loyalist agents “look[ed] like choirboys”, as one ex-Branch officer put it.

How was it that such collusive relationships were allowed to develop in the first place? We now know the answer: there were no proper rules for counter-terrorist agent handling operations. And for the Northern Ireland intelligence-gathering agencies this posed a dilemma that had never confronted Britain when it was fighting its small colonial wars because in places like Cyprus and Kenya there was no domestic media to account to, and the victims were not British citizens.

For Northern Ireland security ministers like Michael Mates (who had also served in the province as a soldier), confronting for the first time a terrorist threat from within our own shores “carried out by people who were our own citizens” (even though they saw themselves as Irish) posed a “unique set of challenges as to what to do with things like agent-handling”.

As head of the Special Branch in Belfast, Ray White confronted Mrs Thatcher directly with this dilemma when she visited the city in the late 1980s.

“I just took the opportunity almost off the cuff: ‘Well, Prime Minister, I would welcome detailed guidance and regulation in relation to what we do’,” explains White. “We were operating in a very grey area in which there was no case law. As a police service, we were making up guidance for ourselves as to how we should morally and professionally behave ourselves and live within the law.”

The then RUC Chief Constable Sir Jack Hermon also asked ministers to provide an agent-handling legal framework. MI5 Director General Sir Patrick Walker also raised this with Mrs Thatcher. Yet such a framework was only finally agreed 13 years later in 2000, two years after the Good Friday Agreement. “The facts speak for themselves,” says today’s PSNI Chief Constable George Hamilton.

Officials did make a stab with a draft framework in 1992 — five years after the matter was first raised — but it was so ineffectual that in a handwritten note the Solicitor General, Sir Derek Spencer, wrote: “the thrust of para[graph] 4 appears to be ‘Don’t get caught’! This is unpromising territory for Ministerial approval.”

Despite the security services’ request for a framework, they don’t appear to have pressed the case home to ministers with much urgency. Nor, it seems, did ministers see the need to respond in a hurry. That amounts to a “wilful and abject failure by successive governments”, concludes the former UN chief war crimes prosecutor Sir Desmond De Silva QC, in a review commissioned by David Cameron of Patrick Finucane’s assassination. According to Mates, the security services “thought it would be better if ministers didn’t know the fine detail of these things because they might be asked to account for them and if they didn’t know they could say they didn’t know”.

However, the state’s failure to regulate agent-handling during the conflict has given credence to Adams’s mantra that there should be “no hierarchy of victims”, by which he means an IRA man shot dead by the security forces while attempting to commit murder in cold blood is as much of a victim as anyone murdered in cold blood by a terrorist. Yet when it comes to accountability, Adams seems quite happy for there to be a hierarchy — again, in the IRA’s favour.