At a gathering to commemorate the IRA hunger striker Bobby Sands, Mr McDonnell said: "It's about time we started honouring those people involved in the armed struggle. It was the bombs and bullets and sacrifice made by the likes of Bobby Sands that brought Britain to the negotiating table. The peace we have now is due to the action of the IRA."

A Labour spokesman distanced the party from Mr McDonnell's comments, but refused to comment on whether he would face disciplinary action over his remarks.

"These views do not represent the views of the Labour party," he said. "The Labour party unreservedly condemns all atrocities perpetrated by the IRA and other paramilitaries."

Since winning the marginal seat of Hayes and Harlington in 1997 Mr McDonnell has been a thorn in the side of Tony Blair and the Labour leadership. He is currently chairman of the resolutely un-Blairite Socialist Campaign Group of MPs and was a vociferous critic of war in Iraq.

Contacted later by the Sun, Mr McDonnell stood by his words. "The deaths of innocent civilians in IRA attacks is a real tragedy, but it was as a result of British occupation in Ireland," he told the tabloid.

"Because of the bravery of the IRA and people like Bobby Sands we now have a peace process."

The leader of the Ulster Unionist party, David Trimble, called for Mr McDonnell to be expelled from the Labour party.

He said: "Mr McDonnell's remarks about the IRA, apart from being completely wrong, are crass, insensitive and an insult to the thousands of British people, police and servicemen who have been murdered, maimed or bereaved by the actions of these terrorists."

"To label terrorists as brave and to lay blame for the murders, bombs and beatings of Irish republicans at the government's door is a disgusting accusation. Mr McDonnell's statement is much worse than any comments made by George Galloway.

"He should be expelled from the Labour party immediately."

The shadow Northern Ireland secretary, Quentin Davies, condemned Mr McDonnell's comments, saying it is "almost unbelievable that an MP should heap praise on those who have murdered our fellow citizens".

Nigel Dodds, MP for the anti-Good Friday agreement Democratic Unionist party, called on the Labour party to discipline Mr McDonnell for "lauding and praising murderers and terrorists".

"Mr McDonnell should remember that the IRA murdered not only soldiers and policemen but men, women and children and I think the Labour party should be taking strong action against him," he said.

Though the Labour party was happy to condemn IRA "atrocities", it was careful to offer some praise for the Sinn Fein president, Gerry Adams, who has steered the republican movement through the peace process.

A Labour spokesman said: "Progress over the last five years since the Good Friday agreement has been enormous, life has measurably improved for people in Northern Ireland."

"Although the postponement of the election [which were due to take place yesterday] was enormously disappointing, even in the last six months progress has been made on all sides. The IRA statements, and the clarifications offered by [Mr] Adams, represented progress by the republican movement."

"However, the government does not feel that the IRA has yet made clear that it is prepared to cease all paramilitary activity fully and permanently," he concluded.

Mr McDonnell lists "generally fermenting the overthrow of capitalism" among his interests in Who's Who.