The security forces protected “state sponsored serial killers” on both sides of Northern Ireland’s paramilitary groups who are responsible for some of the most notorious unsolved murders of The Troubles, according to a BBC Panorama documentary.

Britain’s Secret Terror Deals claims it is the first time the scale of the UK’s counter-intelligence efforts have been revealed.

The murder of Sunday World reporter Martin O’Hagan in 2001 and two massacres, at Sean Graham bookmaker’s in 1992 where five people died, and the killings of nine Protestant men returning from work in Kingsmill village in 1976, are among the cases where state and paramilitary collusion is alleged to have been covered up.

Panorama also revealed an assault rifle used in the Sean Graham massacre, which police said had been disposed of, ended up on display in the Imperial War Museum.

The programme also said the state paid an agent who helped develop a new IRA bomb that killed 34-year-old married RUC officer Colleen McMurray, before all the evidence surrounding her murder in 1992 went missing. The ombudsman’s report into Mrs McMurray’s death is yet to come out. It is one of dozens of ongoing investigations surrounding unsolved murders where state collusion with paramilitary groups is alleged.

George Hamilton, Chief Constable of the PSNI, told Panorama he “entirely refuted” the suggestion that officers colluded with Mr O’Hagan’s killers and that the police pursued many people within “the terrorist organisation… and locked many of them up”.

The Police Ombudsman’s report into Mr O’Hagan’s death was delayed because the Police Service of Northern Ireland refused to release “crucial” intelligence files. In total, police refused to hand over documents relating to 60 murders – the state has been accused of involvement in all of them.

Panorama said it had uncovered “extraordinary evidence” to show how the victims were killed and their killers protected.

Baroness Nuala O’Loan, the former Police Ombudsman Northern Ireland, said: “When I first heard about it I didn’t think that could be possible. [The state] were running informants and they were using them and the argument was that by so doing they were saving lives. But hundreds and hundreds and hundreds of people died because those people were not brought to justice and weren’t stopped in their tracks… Many of them were killers and some of them serial killers.”

Only when the current Ombudsman Dr Michael Maguire, threatened to take the police to court did the PSNI release the files. His investigation into Mr O’Hagan’s death has been ongoing for eight years.

Raymond White, retired RUC Assistant Chief Constable and former Special Branch Officer, admitted to the programme the state “recruited people with blood on their hands” in order to save lives.

He said: “That’s what we were employed to do, to get information and the best information comes from within organisations. That’s the reality of the life in which we lived.”

The Government told the programme the “vast majority” of those who served with the security forces “did so with distinction”. It has previously apologised for previous cases where collusion has been proven.

Amnesty International’s Northern Ireland Programme Director Patrick Corrigan said: “The breadth and depth of collusion being alleged here is truly disturbing. Killing people targeted by the state, using intelligence provided by the state and shooting them with guns provided by the state - if all this is proven, we’re not talking about a security policy we’re talking about a murder policy.