Members of the Force Research Unit, the arm of the army’s intelligence corps that handled undercover agents, including Freddie Scappaticci, known as ‘Stakeknife’, during the Northern Irish Troubles

The head of MI5 is to answer police questions about the activities of Stakeknife, one of the British Army’s most precious moles in the IRA during the Troubles, who is under investigation for 17 murders.

Sir Andrew Parker, director-general of the Security Service, will be asked to make a statement detailing his agency’s knowledge of Stakeknife’s alleged crimes after detectives uncovered a cache of secret documents at Thames House, MI5’s London headquarters.

Police officers working on a £35m inquiry into alleged collusion between British intelligence officers and the IRA double agent over three decades have set up a permanent unit in MI5 after the discovery of the previously undisclosed material, some of which is understood to be held on antiquated microfiche.

Detectives from Operation Kenova,