Furious Labour politicians warned Tony Blair last night that they had drawn a line in the sand over the American request for the deployment of more British troops.
Previously loyal MPs who had supported Mr Blair in the vote on the war in Iraq said: "This far, and no further."
Government whips reported back to Mr Blair of their alarm at the change of mood on the Labour back benches. "The worm has turned," said one anti-war Labour MP.
Geoff Hoon, the Defence Secretary, was also being blamed for mishandling a holding statement on the deployment of troops after making it clear that Mr Blair could not say "no" to President Bush. "He made a bad mistake," said one minister.
Labour MPs were threatening to take their protests to the Prime Minister, saying they were being treated with contempt by the Government. Mr Hoon had made clear that they would not have a chance to vote against the deployment of British troops.
The change of mood among Labour MPs marked a turning point at Westminster.
Mr Hoon went to the Commons to announce that a UK reconnaissance team would visit the area today to report back to the Chiefs of Staff tomorrow on the US request, which was made on Sunday, 10 October. He insisted that no decision had been taken but said he expected a final recommendation from the Chief of Defence Staff to be made by the middle of the week.
He infuriated Labour MPs when he told them that if Britain said "no" to President George Bush "we will have failed in our duty as an ally". MPs are incensed that Mr Blair appears to be taking them for granted. Sir Gerald Kaufman, who voted for the war, warned Mr Blair against putting lives of British troops at risk to support the Republican President against his Democratic challenger, John Kerry, in the presidential election on 2 November.
"I have not changed my view on the war but I do not want my government to be manipulated by one of the most unscrupulous US administrations that the US has ever seen," he said.
Many Labour MPs believe Mr Bush wants a decisive victory before polling day, and he needs British troops to relieve US troops before they mount an attack on insurgents in Fallujah.
Andrew Mackinlay, a Labour MP who supported the Government on the war, warned Mr Blair that formerly loyal MPs would not stomach the deployment of troops to help President Bush. "The UK has given 110 per cent on this issue and some of us have provided political cover and support for this Government. I beg him not to stretch the envelope so much it will burst. Some of us will not stomach it," he said.
Mr Hoon, who survived the Hutton inquiry, had been intending to play a "dead bat" over weekend speculation that 650 members of the Black Watch would be deployed to replace American troops in Iskandariyah and Latifiyah, 20 miles south of Baghdad. It would be the first time that British troops have been deployed outside the Basra area and brought under US military command.
The American military on the ground made a formal request to their British counterparts in Iraq for reinforcements to allow US forces to launch a decisive offensive against insurgents in Fallujah. Many believe the assault will come before the American presidential election on 2 November. Some MPs believe Mr Hoon intended to take it to the full Cabinet on Thursday and announce it during a thinly attended defence debate.
He looked unruffled yesterday despite hostility from his own side. He could clearly handle the criticism from the "usual suspects", led by the left-winger Dennis Skinner, who accused Mr Blair of giving "oxygen'' to President Bush. But he was undone by the Liberal Democrat MP Jenny Tonge, over what penalty Britain would pay if Mr Blair said "no". Mr Hoon's reply that Britain would be letting down an ally if it rejected the request led to shouts of anger from his own side.
The families of Black Watch soldiers also expressed their anger after Mr Hoon confirmed that the Government was considering the request for British troops to provide assistance outside the British-controlled southern sector of Iraq.
James Buchanan, 56, from Arbroath, whose sons Craig, 25, and Gary, 27, are corporals in the regiment, said: "My boys know they have to fight but they hate being lied to.
"It's a bloody disgrace how the Government has treated them. They're stabbing them in the back and trying to disband them at the same time."