THE North's First Minister Peter Robinson has threatened to resign unless there is a judicial inquiry into the aborted trial of the man who was accused of the 1982 IRA bombing of Hyde Park in London, which killed four soldiers.
Mr Robinson said he would walk away from government in the wake of the collapse of the trial of John Downey.
He threatened to resign unless there was a judicial inquiry into secret letters given to more than 180 Irish republican paramilitary suspects by the British government.
The Democratic Unionist leader said the contents of a motion he would put before the Stormont Assembly during a specially convened session tomorrow would depend on how the British government responded to his demand.
Taoiseach Enda Kenny's top officials are understood to be closely monitoring the escalating crisis in the North.
Mr Robinson said he was not prepared to remain as first minister in a power-sharing government "kept in the dark" about such an important matter.
He was speaking after the trial of Mr Downey, from Donegal, collapsed earlier this week.
"To this present day, no secretary of state... nobody mentioned to me that these letters had been sent out to 187 or more individuals, as it may well turn out to be. I think that is astounding, I think it is despicable that the government should behave in such a way," he said.
However, British Defence Minister Anna Soubry, a former barrister, said there was no chance of a judicial review.
She said: "You can't judicially review the decision. So, with great respect to Peter Robinson, unfortunately, I cannot see any way back from where we are now."
She acknowledged that Mr Robinson "is quite right to be very angry, absolutely right to be angry, but we are in a very, very unpleasant, bad situation".
While the mistakes that resulted in Mr Downey receiving the letter have led to an apology from the Police Service of Northern Ireland (PSNI), a political crisis has erupted at Stormont on the wider issue of why the government was sending out any assurance letters, allegedly without the knowledge of the majority of Stormont politicians.
The deal was apparently struck between Sinn Fein and the previous Labour government after an effort to legislate on the issue of on-the-runs (OTRs) failed.
But of 187 letters sent out, 38 were issued since the coalition government took power in 2010.
It also emerged that the North's Justice Minister David Ford knew nothing about the letters and is reportedly furious.
Last night, the Department of Foreign Affairs issued a brief statement. It said: "The thoughts of the Government are with the families of those killed in the Hyde Park bombing on July 20, 1982.
"The judgment further underlines the urgency of making progress in the talks between the party leaders in Northern Ireland on establishing more effective arrangements for dealing with the past and for addressing the needs of victims."
A judge ruled on Tuesday that Mr Downey (62) should not be prosecuted for the Hyde Park attack. It emerged he had received an official letter in 2007 assuring him he would not face prosecution if he re-entered Britain.
The letters were part of the 1998 Good Friday Agreement.
Mr Downey was charged with killing four cavalry soldiers in the Hyde Park bombing by the IRA. Seven military bandsmen were also killed in a separate bombing on the same day on July 20, 1982, in London's Regent's Park.