Victims of the IRA Birmingham pub bombings have reacted furiously to claims that police sent secret letters promising two people that they would not be prosecuted.

Paddy Hill received a life sentence for the atrocity but his conviction was later quashed.

He said two people the IRA claimed were involved were told they would not face prosecution for the 1974 attacks which killed 21 people. His allegations are to be raised with the West Midlands chief constable by the local police commissioner.

Julie Hambleton, whose sister Maxine died, said: "We are incandescent with frustration, anger and more grief.

"It is almost as if we are re-living the horrors of losing our sister all over again and being slapped in the face."

Letters sent to around 200 IRA on the runs informed them that they were not wanted by police. The Government insists these did not constitute immunity from prosecution.

The Northern Ireland Office (NIO) scheme emerged during the collapse of the trial of alleged Hyde Park bomber John Downey after police mistakenly sent him one of the letters even though he was sought by the Metropolitan Police.

Mr Hill told the Birmingham Mail: "I think it was about 1980 that I was told about the IRA claiming five people were involved in the Birmingham bombings. I understand two have since died. They never named anyone.

"I understand that two of these men received letters from the British Government, telling them they would not be prosecuted. One of the five has not received such a letter. The two others have died."

He added: "Many people are sweating, not knowing what's going on. It might prevent further admissions of guilt because they will now wonder if they will face prosecution."

Northern Ireland's power-sharing government, established after the 1998 Good Friday peace agreement which largely ended the 30-year conflict, was thrown into crisis by the Downey revelations last Tuesday.

The oyster farmer, 62, from County Donegal, had pleaded not guilty to the murder of four soldiers from the Household Cavalry who died in the blast on 20 July 1982 along with seven of their horses.

The bomb had been concealed in a car and was detonated as the soldiers rode past on ceremonial duties.

He was detained in May last year at Gatwick airport en route to Greece and spent nine months in custody awaiting trial.

But he dramatically walked free after an Old Bailey judge stopped the case because a letter had been erroneously sent to him from the Government prior to his arrest saying he was not wanted by the police.

The message, which gave no guarantee that future evidence would not emerge linking him to Hyde Park, was sent as part of political talks between Sinn Fein and Tony Blair's administration linked to the consolidation of the peace process.

The revelation that many others received similar letters prompted outrage from victims of terrorism who branded them "get out of jail free" cards.

Democratic Unionist First Minister Peter Robinson said he had been kept in the dark and threatened to resign. He withdrew the threat after Prime Minister David Cameron ordered a judge-led inquiry.

Nobody has been brought to justice for the killing of 21 and injuring of 182 people in Birmingham on November 21, 1974.

Mr Hill was jailed for the Birmingham pub bombings in 1975 along with Hugh Callaghan, Gerard Hunter, Richard McIlkenny, William Power and John Walker.

The Birmingham Six, as they became known, spent 16 years in prison before their convictions were quashed in 1991.

Ms Hambleton told BBC Radio Ulster she was outraged at Mr Hill's claims and said the victims had been slapped in the face by those who were meant to protect them.

"It just beggars belief. The benchmark of any civilised society can be measured by the quality of its justice system," she added.

"The on the run letters have made an absolute mockery of our justice system."

Bob Jones, West Midlands police and crime commissioner, yesterday tweeted: "Will raise with cc tomorrow. I have not heard of these letters other than via news."