A former agent inside the IRA has demanded a review of ballistic evidence gathered when he was shot in England in 1999.
Martin McGartland suspects ballistic records were altered to obscure republican involvement in his attempted murder in Northumbria.
He has written to PSNI Chief Constable Matt Baggott, as well as the Northumbria Chief Constable Sue Simm and Police Ombudsman Dr Michael Maguire, to raise his concerns.
"I have stated since the day of my shooting that Northumbria Police, PSNI and Police Ombudsman's office have all been party to a sophisticated cover-up.
"I say this has been on the orders of MI5 and the State and that they have been protecting Provisional IRA terrorists involved in my kidnapping and my 1999 attempted murder," he claimed.
Mr McGartland wrote after the Weapons and Explosives Research Centre (WERC), a Northern Ireland agency which maintained ballistic records, was heavily criticised by the judge at a recent Belfast inquest.
Mr Justice Weir was presiding at an inquest into the murder of Roseann Mallon, a Tyrone pensioner gunned down by the UVF in 1994.
WERC told the police that the Kalashnikov rifle used had no previous history.
However, an Historic Enquires Team review found that it had been linked to incidents involving at least 11 further murders.
Mr Justice Weir questioned the abilities of the unit, calling it "a forensic system within a forensic system".
Mr McGartland was shot six times as he got into his car in 1999 and was not initially expected to survive. He is disabled as a result.
After the shooting, Northumbria Police documents show that two handguns were discovered near Gateshead. One was identified as the gun used to shoot him.
Both guns and cartridges were sent for examination by WERC which ruled out their use in any previous shootings.
At the time RUC detectives contradicted this.
They told the Belfast Telegraph that the same batch of homemade bullets used to attack McGartland had been used in the murder of Brendan 'Speedy' Fegan, a Newry drugs dealer.
Republicans had been clearly linked to that shooting.
Mr McGartland pointed out that when he was unconscious in hospital, Northumbria Police briefed journalists his shooting had no connection to Northern Ireland, and instead linked it to an alleged dispute with drug dealers.
After recovering he sued the police, who apologised and paid him compensation, as did several newspapers who carried the defamatory report.
The Belfast Telegraph has learnt that WERC was renamed Centre for Information on Firearms & Explosives (CIFEx) in 2009.
A PSNI spokesman said its role was to provide "firearms and explosives-focused scientific support to the Police Service".
Martin McGartland is a west Belfast man who infiltrated the IRA as a police agent between 1987 and 1991.
When his cover was blown he was abducted, but escaped by jumping from a third-floor window in Twinbrook's Broom Park.
He took the name Martin Ashe and resettled in Tyneside. He was tracked down and shot six times by unknown assailants in 1999.
He now lives elsewhere under another identity. His story was the subject of the 2009 film, Fifty Dead Men Walking.