Mr Tony Blair has rejected Conservative demands for a halt to terrorist prisoner releases in the light of the escalation of so-called "punishment" attacks by paramilitaries in Northern Ireland.
The Prime Minister told Mr William Hague that to do so would in effect "bring the whole of the Good Friday agreement to an end".
But having earlier warned Mr Blair that bi-partisanship "is not a blank cheque", Mr Hague last night threw his weight behind a growing campaign to halt the release of an IRA killer of three policemen on the 10th anniversary of his crime.
In the Commons Mr Hague said the proposed release date for Henry McCartney in July 2000, and of Tarise Connolly, also convicted for the same attack four days later, was "an act of grotesque insensitivity on the part of the Northern Ireland Office".
Mr Fred Sterritt, the father of one of the murdered constables, David Sterritt, last night welcomed Mr Hague's intervention, branding the proposed release date a sickening insult.
During exchanges on prisoner releases which dominated Prime Minister's Question Time, Mr Hague said: "Plans are being made months ahead for the early release of terrorists seemingly without regard to whether any guns or bombs will be turned in."
To Tory cheers he demanded: "Isn't it time we stopped releasing them, that we put on hold for now releasing convicted terrorists when they've not given up a single gun or bomb?"
After a series of disappointing encounters with Mr Blair in recent weeks, there was some surprise at Mr Hague's choice of subject.
But the Conservative leader clearly calculates that his stance on the arms issue is one which will find favour with British public opinion, over the immediate issue of prisoner releases and, even more critically, on the coming issue of Sinn Fein's entry into the Northern Ireland executive.
Citing the case of Mr Andrew Peden "who was tortured for 10 hours, who was left to die, who lost both his legs, whose wife says he cries out every night as he relives what happened to him", Mr Hague challenged Mr Blair to say whether such attacks were a breach of the Belfast Agreement.
The Prime Minister agreed they were. But it was a difficult issue with which the previous Conservative government had grappled during the first IRA ceasefire.
Indeed, Mr Blair said, "they continued their early-release schemes although punishment attacks were going on at the time".
Mr Hague countered that the schemes operated by the last government had not extended to life sentence prisoners and the two were not comparable at all.
The Tory leader quoted the Chief Constable of the RUC who said last Friday: "There is no doubt whatever that all of these organisations, including those who purport to be in cessations of military operations, are engaged in this repugnant activity".
Mr Blair agreed Sir Ronnie Flanagan had made the comments, but added: "He also, however, said that he believed the cease-fires were intact."
Mr Blair said the peace process would present difficulties for whatever party was in government.
To warm approval on his own benches, Mr Blair recalled that Labour in opposition had supported the initial Tory demand that the first ceasefire be declared permanent; they had supported Mr Major's government when its previously denied secret negotiations with the IRA had been revealed; as they had, too, when it first imposed and subsequently abandoned the "Washington Three" test on decommissioning.
The Prime Minister told Mr Hague: "We have to make a judgment. What he is asking us to do would in effect bring the whole of the Good Friday agreement to an end.
"He has to follow through the consequences of what he's saying. We continue to make the judgment we do in difficult circumstances. The consequence of taking the course he is advocating is more serious than he is saying.".