Has Short lost credibility? Click here for analysis

Home Office Minister John Denham has now followed Health Minister Lord Hunt of Kings Heath in resigning on Tuesday morning.

Their resignations come in the wake of Robin Cook's departure from the cabinet after he objected to war without a fresh United Nations mandate.

Ms Short's decision to stay - despite saying she was still "very critical" of the way the crisis has been handled - is a boost for Tony Blair as he prepares to get House of Commons backing for war on Tuesday afternoon.

US President George W Bush gave the Iraqi leader and his sons 48 hours from 0100 GMT on Tuesday to leave Iraq or face invasion.

VOTING ARITHMETIC 165 Labour MPs must rebel before Mr Blair has to rely on Tory votes 245 Labour MPs must rebel for Mr Blair to lose a vote on Iraq, even with Tory support Click here for full text of Commons motion

Mr Blair has pledged the UK's support for war with Iraq but the prime minister knows that he still has to win the support of many of his own MPs - and the voters.

Ms Short, who said she would back the government in the vote on Tuesday, had previously threatened to resign if war began without a new UN mandate.

Announcing her decision to stay, she said in a statement: "I know I will be heavily criticised for my decision and many people will feel I have let them down.

"But I am doing what I think is right in the circumstances which we are now in."

Mr Blair had persuaded America there had to be a new UN mandate for rebuilding Iraq after a war, she said, and there were developments in the Israeli-Palestinian peace process.

An ICM poll for the Guardian suggests public opinion is shifting towards backing war although more still oppose (44%) than back (38%) war.

'Key challenge'

There were two more departures from the lower ranks of government: Bob Blizzard, the parliamentary private secretary to Work and Pensions Minister Nick Brown, and Anne Campbell, who did a similar for Trade Secretary Patricia Hewitt.

Robin Cook's resignation speech late on Monday evening was greeted with an unprecedented round of applause and a standing ovation by some MPs.

Click here for Robin Cook profile Click here for Cook speech in full

Lord Hunt announced he was quitting on BBC Radio 4's Today programme, saying he had agonised over the Iraq policy for weeks.

"I don't support the pre-emptive action which is going to be taken without broad international support or indeed the clear support of the British people," he said.

Deputy Prime Minister John Prescott was dismissive of his resignation - claiming never to have heard of Lord Hunt.

Welsh Secretary Peter Hain said the resignations were a blow.

"But in the end we as a government feel we cannot walk away from this situation, leaving Saddam Hussein unchecked, able in the future to attack the world," he said.

Straw: Crucial debate

Mr Blair held a series of meetings with rebel MPs late on Monday and is addressing the Parliamentary Labour Party ahead of the Commons debate which starts at 1230 GMT.

A vote will then follow after the prime minister asks MPs to authorise the use of "all means necessary" in order to disarm Saddam Hussein.

Home Office Minister John Denham

Mr Cook said he would be one of those opposing the government.

Rebel MPs have drawn up an amendment to the government's motion stating there is no moral justification for war without a new resolution.

The last debate on the Iraq crisis saw 122 Labour MPs voting against the government and rebels say 120 MPs from all parties have already signed the amendment.

Mr Blair has won support from Conservative leader Iain Duncan Smith, who said: "If we do not face up to Saddam now, then frankly, in two years' or three years' time, maybe even sooner, we could find those biological chemical weapons on our doorstep."