We want proof that there is to be an Iraqi attack on the continental United States

Tam Dalyell Labour MP

The move is aimed to coincide with Mr Cheney's visit to London and Ms Mahon said the UK prime minister should stop being the "little lapdog of America".

Ms Mahon's Commons motion expressing "deep unease" at Britain's potential involvement has already attracted the signatures of more than 70 MPs, including several former Labour ministers.

The MP said Britain should not "go down this road that could lead to a third world war."

UN involvement

There are also reports of cabinet divisions over possible action.

Ministers were reported to have told Mr Blair at their weekly meeting that all possible avenues must be explored before any conflict with Baghdad could be considered.

Downing Street on Friday denied reports that one or possibly two ministers might resign if action goes ahead.

It said there was a ''thoughtful, sober discussion in relation to the threat from Saddam Hussein'' at the cabinet meeting.

Dalyell: Proof needed that Iraq is to attack the US

But Mr Dalyell insisted: "If there is to be action it should be through the United Nations and not unilaterally by the United States."

The veteran MP says Iraq's neighbours are begging there to be no bombing campaign.

He argues there should be a vote of MPs before any "land war" is begun.

"Personally, I think we should try talking to the Iraqis," Mr Dalyell told BBC Radio 4's Today programme.

Detailed discussion

He added: "We want proof that there is to be an Iraqi attack on the continental US."

There are signs that some normally loyal MPs are unhappy with the direction of government policy.

Salter says action against Iraq may destabilise the Middle East

Labour MP Martin Salter, a signatory of the Commons motion, said: "I was a staunch supporter of action in Afghanistan, but this is totally different.

"It is just about the Republican right wing in America trying to finish off the job that the first George Bush failed to do. This is to avenge an American audience."

'Unwise and unsupportable'

Mr Salter told BBC News Online that any action led by America would "further destabilise the Middle East".

"There is no international coalition that would support an attack on Iraq," he warned.

"I would not want to see Britain isolated from the rest of the world over an action that is unwise and unsupportable."

Labour's former Armed Forces Minister Doug Henderson said: "Before any action is taken, they (the government) need to demonstrate in a way that is believed by the rest of the world that the situation has deteriorated and there is now a greater danger than there was before."

Mr Henderson also warned that Saddam Hussein might pre-empt any strike on him.

Diplomacy needed

Labour's David Chaytor argued that an attack on Iraq could be "Vietnam, mark two".

Diplomatic efforts needed to continue by the international community to deal with the "problem" of Saddam Hussein.

"It cannot be solved militarily by the US alone," he said.

He did not rule out military action against Iraq, but said it must be carried out by the international coalition.

And he warned Mr Blair: "I just think it is untenable for the British government to be the only supporter of the US in this situation.

"Certainly there is a serious threat that the Labour Party would be split down the middle if the government pushed ahead with its support for the US."