The Black Watch regiment was yesterday ordered by the Cabinet to help US forces throw a "ring of steel" around Fallujah before an all-out assault on insurgents in the city.
The 850-strong 1st battalion, including three companies of armoured infantry, totalling some 500 men, equipped with 50 Warrior armoured troop carriers, is being ordered to hold an approach road into Fallujah, where extremists including Abu Musab al-Zarqawi who is believed to have murdered Kenneth Bigley are thought to have their strongholds.
Robin Cook, the former foreign secretary who resigned over the war, last night warned Tony Blair that Britain will be associated with the blame if the assault on Fallujah resulted in heavy civilian casualties.
There are fears that the number of troops in Iraq is being increased under cover of the moves to replace the 1st Battalion, the Black Watch as the main reserve force, fuelling anxiety among Labour MPs that Britain will be sucked into a Vietnam-style war. Mr Blair denied on Wednesday in the Commons that the number of British troops in Iraq was being increased, but Geoff Hoon, the Defence Secretary, refused to repeat that denial last night when challenged on BBC radio.
Patrick Mercer, the shadow Home Security Minister, accused ministers of "sneaking in the extra troops". He added: "Tony Blair has said he is prepared to pay the blood price. Let us hope that not too many of this battle group have to honour his words."
Mr Blair warned MPs to expect an upsurge in violence in the run-up to the January elections in Iraq. Dissident Labour MPs said last night they feared Britain would be asked again by the US to send more troops.
The role assigned to the Black Watch will also cause anxiety that British troops are being more closely associated than expected with the forthcoming assault on Fallujah. The Defence Secretary indicated on Monday that they would be relieving an existing US unit, but military sources said last night that was not the case. "The Americans are throwing a ring of steel around Fallujah, and are sending in Iraqi forces to do the close fighting. The British and American forces will be in an outer ring of steel," a military source said. "The Black Watch will protect an approach route to the city. They are not replacing an existing American force."
The number of British troops in Iraq is set to rise because the Black Watch will be replaced by an 850-strong force of the 1st Battalion, the Scots Guards with Warrior armoured vehicles.
The Prime Minister's official spokesman said Mr Blair secured the "unanimous" support of the Cabinet for his Iraq strategy. Whips headed off a full-scale mutiny by Labour backbenchers furious at Mr Blair for appearing to put British lives at risk to support George Bush in the US election.
Mr Blair saw a handful of the MPs in one-to-one meetings, including Anne Campbell, the Labour MP for Cambridge, who said he had persuaded her that it was for military, not political purposes. Eric Illsley, a Labour MP who supported the Government in a vote on the war, said: "I still think this is a symbolic gesture to help Bush. It would have been better to delay the whole decision until after the presidential elections."