The deployment of British troops called in to support US forces in central Iraq is under way, the Ministry of Defence said. Soldiers from the Black Watch are moving northwards from their base in Basra to near Baghdad.

The Warminster-based regiment Black Watch has been promised it will be home for Christmas despite hints its soldiers will relieve American troops in a dangerous region of Iraq.

Critics of the proposal to send in Black Watch soldiers to replace US troops near Baghdad have blasted the Government, saying it is a political and not a military decision.

The First Battalion of the Black Watch is based in the British sector of southern Iraq, near Basra.

The US military has requested the 650-strong battalion move to the south west of the Iraqi capital to replace troops earmarked to go into Fallujah to battle insurgents, including those responsible for the death of hostage Ken Bigley.

The Prime Minister Tony Blair promised the Warminster-based troops they would be home for Christmas even if they were switched to replace US forces.

A well-placed Army source told the Wiltshire Times: "It is ridiculous to say the troops will be home by Christmas because of the nature of war.

"If they are not needed in their current position why are they there at all?

"There are 160,000 American troops _ why do they need 650 British blokes?"

West Wilts MP Dr Andrew Murrison, who served in Iraq, is disgusted that the troops are possibly being used for political gain.

He said: "There is a strong suspicion that this development is motivated by the upcoming US elections.

"Geoff Hoon (Secretary of State for Defence) let the cat out of the bag when he said we would be letting down our allies if we refused.

"Clausewitz said that 'war is politics pursued by other means' and this appears to be the case.

"If it is true then this is a gross misuse of a regiment that has already been insulted by this Government and done more than its fair share of duty in Iraq."

Dr Murrison said the Conservative Party is demanding the Government be more honest and open about its decisions.

"UK and US troops handle themselves very differently and I am worried that our people will become victims of the highly aggressive stance that has characterised the American approach to restoring peace in Iraq," he said.

Major Roddy Mellotte, spokesman for Warminster Garrison, said: "The wives of the soldiers here have been absolutely fantastic.

"They all miss their husbands terribly but they have been really stoical about the whole thing."