BBC NI Spotlight examines the intelligence war against the IRA
During the decades of conflict in Northern Ireland, informers and agents were the state's most deadly weapon in a secret intelligence war.
In an exclusive interview with BBC NI's Spotlight, a man who says he was a former spy who brought Special Branch deep within the republican movement, tells his story of betrayal.
For months, I've been in contact with a man, referred to in the programme as "Martin".
Martin says he was an agent of the state inside the IRA and Sinn Féin.
In the programme he outlines when and how he first contacted Special Branch, as well as how he made the transition from being an informer - providing information in a passive sense - to becoming an agent, targeting specific individuals at the request of his handlers and doing exactly what he was told.
Significantly, he tells Spotlight about a particular individual within the republican movement - who he says he betrayed - and the deadly consequences.
In talking to Special Branch, Martin was following in a long line of informers and agents in both republican and loyalist paramilitary groups.
But the scale of infiltration has rarely been acknowledged.
In 2008, Denis Bradley and other members of the Consultative Group on the Past travelled to London to examine an archive of classified government documents.
"It's an archive of most of the Troubles, particularly the big, traumatic events and it's an archive also of that world of intelligence - who was running intelligence and who were the informers and who was in charge of it and so forth," said Mr Bradley.
"At any one time, the security services were running about 800 informers, at any one time throughout the Troubles. Now that's a lot of people within a small community of people."
In fact, security sources have told Spotlight that the figure of 800 is an underestimate, and is closer to the total number of Special Branch informers and agents in Belfast alone.
'Silent damage from the inside'
A well-placed and long-term agent could silently damage the IRA from the inside.
'Agents of influence' were among the most valuable assets of British intelligence inside the IRA - individuals whose value was the subtle influence they could bring to bear when key decisions were being taken by those at the top of the IRA.
"The IRA was broken up into about nine different structures or levels of operation" said Raymond White, a retired RUC assistant chief constable and Special Branch Officer.
"So agents had to be selected and, if possible, placed or manipulated into certain positions and allowed to develop and grow."
"If you looked upon agents and those, they're sort of a cancer within, a slow-growing cancer - they can sort of infect other parts of the system."
Tuesday's Spotlight investigates the secret intelligence war between the state and the IRA and has gained a unique insight into the world of intelligence gathering and targeting.
- Spotlight is on BBC One NI at 22:45 BST on Tuesday.