A former British agent who infiltrated the IRA says an internal police report has finally confirmed that he was targeted and shot by the group in a murder plot that he alleges was covered up by the government.

The Guardian has seen a copy of a review by three forces into Northumbria police’s investigation of the 1999 attempted murder of Martin McGartland.

McGartland was recruited by the RUC special branch to infiltrate and undermine the Belfast IRA in the late 1980s. His exploits were later turned into the film Fifty Dead Men Walking starring Jim Sturgess and Ben Kingsley.

The police document is a “major crime unit investigation review” by the Bedfordshire, Cambridgeshire and Hertfordshire forces.

Its findings appear to support McGartland’s claims over the past two decades that the IRA rather than a local north-eastern criminal gang was behind the murder attempt in Whitley Bay on 17 June 1999.

In the days, weeks and months after McGartland was shot and seriously wounded, both Northumbria police and the then Labour government refused to confirm that the IRA was responsible.

McGartland, along with unionist politicians at the time, alleged that the truth was covered up to keep the IRA and Sinn Féin wedded to the fledgling post Good Friday agreement peace process.

In their review, the three constabularies led by Jon Boutcher, the ex-Bedfordshire chief constable and head of another multimillion investigation into another army spy in the IRA – Stake Knife – concluded that republican paramilitaries did try to kill McGartland.

Among 60 recommendations to the Northumbria police regarding the McGartland shooting, the police forces suggest: “That Northumbria police must make a formal media release acknowledging the re-investigation of the attempted murder of Mr McGartland. This should be underpinned by a public statement that the original shooting was most likely associated with Mr McGartland’s background within the IRA and having acted as an agent of the security services within the republican areas of Belfast and was carried out by a paramilitary active service unit.”

The report also dismisses any suggestion that the shooting was connected to a dispute between McGartland and drug dealers in north-east England. McGartland has always alleged that this line of inquiry was “invented and fed” to media sources by either MI5 or elements of the Blair government to deflect from the IRA’s role in the botched assassination.

“The review has not uncovered any credible evidence of a specific threat to the victim at the hands of ‘local criminals’ or indeed that gives any indication of this being related to any of the victim’s business, his work or his private life within the locality,” the report says.

In addition to calling for a fresh investigation into the 1999 attack on McGartland, the review suggests that “NP (Northumbria police) to consider external force to progress investigation in its entirety”.

Furthermore, it recommends that “key roles” in that fresh investigation “should be filled by persons not connected to NP (Northumbria police)”.

The report also appears to suggest that the IRA line of inquiry was known to the Northumbria police in the immediate aftermath of the shooting.

“Most critically, he (an officer named only as Police R by the review) was of the considered view that the attack was most likely carried out by the Provisional IRA and that this fact was known to the original SIO (senior investigations officer) within a very short timeframe following the attack. He (Police R) would offer no explanation as to why this had not been acknowledged much earlier within the investigation, and that this remained as a significant issue between the victim and the police,” the report says.

McGartland told the Guardian that this finding in particular proved that from the outset officers in Northumbria police knew that the IRA was behind the shooting. The ex-spy insisted this line was “covered up and obscured by false, malicious lies” by senior figures in the security and political establishment to conceal the IRA’s role at a delicate stage in the peace process.

On the report’s main findings, McGartland said: “I am now urging the current chief constable of Northumbria police to immediately admit and acknowledge that the IRA had been behind my June 1999 attempted murder. I am also calling on him to swiftly agree to an external police force to carry out my unsolved attempted murder investigation. I have absolutely no trust, faith or confidence in Northumbria police nor its crime department or any of its chief or senior officers when it concerns me and my cases.”

A spokesperson for Northumbria police said: “We can confirm this case has remained open since the shooting in 1999. Following a recent review, the force are investing a significant and dedicated resource into progressing the investigation.

“The classification of the incident is currently under further review.”

The Northumbria police at this stage however has declined to confirm or deny that the van believed to have been used by the gang that shot McGartland has since been destroyed.

On the wider implications of the report’s findings, McGartland added: “The Northumbria police knew the IRA had been behind my shooting, that they acted in consort with MI5, the Home Office and the then Blair Labour government (and subsequent governments) covered it up to protect not only the IRA as an organisation but the individual IRA members who tried to murder me. And this was done as part of a secret deal between police, security service and government as a result of the Good Friday peace agreement.”

In 1999 McGartland was shot six times by two gunmen outside his home in Whitley Bay, North Tyneside.

Eight years earlier the Belfast-born agent became the only person ever to escape from the IRA’s notorious internal mole hunting unit, the so-called “Headhunters” or “Nutting Squad”.

McGartland dived out of a third storey flat in west Belfast where the IRA were holding him before he was to be handed over to the head of the Provisionals’ security team which was led by a man named Stake Knife, one of Britain’s most important agents inside the republican terror group.