Former IRA members who were given guarantees and letters of comfort that they would not be prosecuted for old crimes are now the target of new Northern Ireland police inquiries.

If they are arrested and tried it would cause a massive crisis in the peace process as the letters from former Prime Minister Tony Blair were taken as immunity documents by the IRA and the men and women known as OTR’s or 'On the Runs.’

But now the Daily Telegraph reports that senior police officers have identified six alleged former IRA men and intend to prosecute them as they no longer believe the Blair letters afford the OTR's any protection.

Fifteen years ago, as part of the final negotiations in the peace process, Tony Blair and Sinn Fein leader Gerry Adam reached agreement on an effective amnesty for up to 200 IRA operatives active during The Troubles.

Blair has been adamant ever since that without the letters of comfort the IRA ceasefire would never have held.

Blair told MPs investigating the scheme: "The issue of OTRs was absolutely critical to the peace process and at certain points became fundamental to it...” Blair stated that without the letters “I think it is likely that the process would have collapsed."

One of the OTR  men, John Downey, was arrested and charged in 2013 with the London Hyde Park bombing in which four British soldiers were killed, but the case against him collapsed after the letter of comfort was revealed.

The Telegraph says that the “dramatic development comes on the eve of a major new report following a year-long parliamentary inquiry into the 'comfort letters' scheme.”

A source close to the inquiry said the “comfort letters” scheme was “chaotic” and “reckless to the point of unlawful.”

In the letter, seen by the Telegraph, Will Kerr, the PSNI Assistant.Chief Constable stated, “Whilst prosecutorial challenges may still lie ahead, the obstacles to investigating, arresting and charging suspects appear to have been removed.”

In a statement the PSNI said it could not give further details of the six new cases. Mr Kerr said: “The review of these cases is an ongoing process. This does involve active criminal investigations and it would therefore be inappropriate to comment further at this stage.”

If prosecutions commence despite the comfort letters it will likely cause a major crisis in the peace process with Sinn Fein left vulnerable to charges by hardliners they did not fully protect their former IRA colleagues.

Former PM Tony Blair says sending letter to suspect of IRA Hyde Park bombing was a mistake.Getty Images