Ben Griffin will join established opponents of the US-led invasion of March 20, 2003, plus family members of some of the 103 British service personnel who have been killed in the Gulf, the Stop the War Coalition said.

The 28-year-old, who detailed his reasons for quitting the elite 22 Special Air Service to a British newspaper last Sunday, expanded on his comments Thursday, calling on Britain to pull out its 8,000 troops immediately.

"Britain has let itself down by following America into this war. They should withdraw from the coalition immediately," he told a London news conference ahead of the protest Saturday in the British capital.

Griffin, who in his two years in the SAS served in Iraq, Afghanistan, Northern Ireland and Macedonia, told his commanding officer of his moral objections last year and was discharged with an exemplary service record.

Since publicly voicing his reasons for quitting, he said he had received messages of support from serving British officers, many agreeing with his view that the war was illegal, and sharing his concern at Britain's perceived lack of influence over US policy in Iraq.

"I think there is a growing feeling in the British Army of disappointment that we're out there and that they feel let down by the government," he said, stressing he had not signed up "to conduct US foreign policy".

Griffin, from London, said he was concerned before being posted to Iraq about the legality of the war and its justification that former Iraqi president Saddam Hussein had weapons of mass destruction, but followed orders and went.

"The conduct of the war, I thought, was wrong. A lot of things were going wrong out there," he explained.

"My views became clearer and stronger while I was serving out there until I reached a point when I found I couldn't separate those views from my job."

Most were linked to the attitude and actions of US forces, whom he said "failed to grasp" the difference between combat and counter-insurgency operations after the end of formal hostilities.

They made little effort to minimise civilian casualties, did not respect rules of engagement to fire only as a last resort and treated the Iraqi people with contempt, he claimed.

They also ignored British advice, gained through harsh experience in Northern Ireland, about not being heavy-handed, all of which had led to the coalition, and specifically the United States, losing Iraqi consent, the soldier stated.

"If you lose the consent of the Iraqi people, there's no way this is going to be resolved until the US and Britain get out of Iraq," he said.

Lindsey German, convenor of the Stop the War Coalition, told AFP she expected up to 100,000 people at the demonstration, which coincides with others around the world, including in Iraq.

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