Senior PSNI police engaged in a cover-up to protect an IRA informer involved in the Remembrance Sunday bombing, one of the most controversial tragedies of the conflict, according to a report in the Sunday Times.

Suspicions have grown in recent years of a British ‘dirty tricks’ agenda in the 1987 bombing in Enniskillen, County Fermanagh, in which 11 people were killed.

Outrage over the attack dealt a major blow to the Provisional IRA, and commemorations of the event are still attended every year by senior Dublin government figures.

A book by author Martin Dillon earlier this year published detailed claims from a member of MI5 that the spy agency had tampered with the bomb before it went off.

And it was revealed this week that cold case team investigating the attack identified an alleged informer as a key line of inquiry - but a proposal to question him was not supported by senior figures in the PSNI.

A former investigator on the PSNI’s now-defunct Historical Enquiries Team (HET) of the Enniskillen bombing said: “It stank. It absolutely stank.”

A new podcast series, The Poppy Day Bomb, has alleged that the man in question had worked as an informer for Royal Ulster Constabulary (RUC) Special Branch, the intelligence division of the PSNI’s forerunner.

The man was arrested 13 years later in 2000 in a related investigation, when he had become affiliated with the breakaway Real IRA - but he fled the country in mysterious circumstances shortly afterwards and has not been seen in Ireland since, according to the report.

The senior investigator who was tasked with investigating the Enniskillen bombing said that a “big question mark” hung over the individual. When he went to others in the force with plans to question him, he said they became “very nervous” and the idea was not supported.

During the investigation, the PSNI’s intelligence unit refused to provide information about the individual.

The investigator, who says he was already in conflict with his bosses about the approach being taken by the HET, was eventually moved off the Enniskillen case.

The HET concluded its report into the Enniskillen bombing in 2012 but families were only given a draft copy in 2017, years after the unit had been shut down amid criticism. The report featured sections that were still censored and incomplete.

In The Poppy Day Bomb podcast, reporter Mario Ledwith also notes that the Crown Forces did not search the building where the bomb was placed during a sweep on the day of the incident - and suggests that may have been deliberate.

The podcast also reveals the RUC ‘investigation’ was downgraded three weeks after the bomb. The investigation remained open, but resources given to it in the immediate aftermath were moved elsewhere within weeks.

It was also revealed that crucial documents which could provide information on the bomb were declared “lost”. The disappearance of the files was blamed on an “asbestos clean-up operation”, a regular British excuse for the destruction of collusion-related files.