The bitter exchanges over the airwaves today exposed the depth of the divisions on Labour's backbenches over the Iraqi question.

Warning that MPs could be accused of "stabbing British forces in the back" if they failed to discuss the issue, Mr Dalyell said that the decision to recall parliament in September should be taken now.

But Labour colleague David Winnick branded Mr Dalyell "an appeaser", claiming most of the Labour benches would support an invasion.

The exchanges on his own benches will only reach the prime minister, who is on holiday in southern France, second hand, but they come as the aircraft carrier Ark Royal sails for the Meditarranean - although the navy claims this is merely part of an exercise. The carrier, with a full complement of Harrier jets and helicopters, will be accompanied by a Type 42 destroyer.

Also today the long-standing Labour critic of Middle East policy, Glasgow MP George Galloway, arrives in Iraq for a personal fact-finding mission. A letter from the parliamentary No War on Iraq group was published in today's Guardian, calling on weapon inspectors to be sent to Iraq, following Saddam Hussein's offer last week.

Mr Dalyell, MP for Linlithgow, told the BBC: "Parliamentary colleagues have to understand this is the most important decision of their political lives and all of us have to stand up and be counted on our judgment.

"None of us can shelter behind a three-line whip on this issue."

He said the government should not ignore warnings from Jordan about the dangers of participating in a US-led attack on Iraq.

"Very important questions remain unanswered," he said.

"What will happen to oil prices? Are we ready to discard the views of our best friends in the Middle East, such as King Abdullah of Jordan, who says it is opening Pandora's box, and so it is." Mr Winnick, the Walsall North MP and a member of the home affairs select committee, argued: "In my view a lot depends on whether Saddam Hussein allows weapons inspectors to go back into the country and without any kind of hindrance whatsoever.

"That would certainly undermine the desire for military action among many people, but I doubt if that is going to happen, so I think war is inevitable.

He said of Mr Dalyell: "As far as my parliamentary colleague is concerned, it should be borne in mind that he totally opposed the liberation of Kuwait and the action in Kosovo and Afghanistan.

"With the greatest respect to Mr Dalyell he is an appeaser of military and criminal dictatorships - which he has every right to be.

"It is not because he approves of those regimes but because he will not accept any military actions.

"Had we listened to those critics in the past just imagine what would have happened.

"The ethnic cleansing would have carried on and Afghanistan would have been under the same criminals who were responsible for September 11.

"Therefore I think we should not take what they say too seriously."

If Iraq refused to admit UN weapons inspectors then there would be an overwhelming case in favour of military action, he said.

"We are dealing with one of the most murderous regimes in the post-1945 period," said Mr Winnick.

But he agreed that parliament should be recalled if there was to be military action.

Yesterday Mr Dalyell wrote to Mr Blair, asking if he did not have a "moral obligation" to recall parliament - which is now in its summer recess - in early September.

His letter followed a warning from a former chief of defence staff that Britain risked being dragged into a "very, very messy and long-lasting Middle East war" if it went along with US plans for a military assault on Iraq.

Field Marshal Lord Bramall called on the government to exercise caution, warning that an invasion to topple Iraqi dictator might not be morally or legally justified.

In his letter, Mr Dalyell said: "In circumstances in which a distinguished chief of the general staff feels obliged to draw ominous parallels with Suez, 1956, and warn of a very messy and long-lasting Middle East war; in which 10 trade union leaders in a letter to a newspaper express their extreme concern; and in which an increasing number of your own parliamentary colleagues wonder about the legality of a pre-emptive strike on Iraq without a fresh and specific UN mandate, do you not have a moral obligation to ask for the recall of parliament in early September?"

Mr Dalyell added: "It is always supposedly too early to make a decision to recall parliament - until it is too late."

The US president, George Bush, earlier dismissed an offer by Baghdad to hold talks on the possible readmission after four years of United Nations weapons inspectors.

"Nothing's changed," said Mr Bush. "I'm a patient man. I'll use all the tools at our disposal."

US arms control minister John Bolton confirmed that "regime change" in Baghdad remained American policy, whether or not Saddam let the inspectors back in.

Britain and America say Saddam has revived his nuclear, chemical and biological warfare programmes following the 1998 withdrawal of the inspectors tasked with finding and eliminating them.