David Cameron, the British prime minister, has announced an independent inquiry into secret letters sent to Irish Republican Army (IRA) suspects which promised them protection from arrest.
The move on Thursday came after a backlash following the release of John Downey, an IRA suspect accused of a 1982 bombing that killed four soldiers in London, who walked free from a London court this month because of such a letter.
Cameron said on Thursday that it was clear that there had been a "dreadful mistake" in the case of Downey, and said that an independent judge with full access to government files and officials would lead the review and report back by the end of May.
Peter Robinson, Northern Ireland's first minister, called off a threat to resign after the inquiry was announced.
Theresa Villiers, Britain's minister for Northern Ireland, said the letters - 187 of which have been sent as part of a 1998 peace deal - state that the recipients are no longer being sought for prosecution. However, they do not amount to immunity from arrest.
"We will take whatever steps that are necessary to make clear ... that any letters issued cannot be relied upon to avoid questioning or prosecution for offences where information or evidence is now or later becomes available," Villiers said in a statement.
The IRA, the military wing of Northern Ireland's Sinn Fein political party, ended its armed struggle against the British in a 1998 peace deal.
More than 3,600 people died, including more than 1,000 members of the British security forces, in decades of violence.
The province is still deeply divided between Protestants, who generally want to remain part of Britain, and Catholics, many of whom favour unification with the Republic of Ireland. Sporadic outbreaks of violence continue to occur.
Secret deal revealed
A London court judgement revealed on Tuesday that Sinn Fein had cut a secret deal.
The judge revealed that governments led by Tony Blair, Gordon Brown and Cameron had provided 187 former-IRA members with official letters vetted by police and prosecutors.
The notes reassured them they would not be arrested for IRA activities if they returned to the UK.
Downey, 62, from County Donegal in Ireland, was arrested last year at Gatwick airport and charged with murdering four members of the Royal Household Cavalry in a bomb attack 32 years ago in Hyde Park, London.
Downey's defence argued that his trial should not go ahead because he had received a letter of assurance from the Northern Ireland Office in 2007 that he was not wanted in connection with the attack.
The presiding judge at the Old Bailey court ruled that the letter, a false assurance, was a "catastrophic failure" that misled the defendant and ruled that the trial would be an abuse of executive power.
Cameron said it was important to find out the facts.
"There was never any amnesty or guarantee of immunity for anyone and there isn't now," he said.
"It is right to get to the bottom of what happened."