Among those on the march was Lance Corporal Joe Glenton, 27, a member of the Royal Logistics Corps who has served in Afghanistan before, but now is facing a court martial for refusing to return.
"It is distressing to disobey orders, but when Britain follows America in continuing to wage war against one of the world's poorest countries I feel I have no choice," he said in a statement issued before the protest.
Britain has 9,000 troops in Afghanistan as part of an international coalition following the US-led invasion in 2001. Most are deployed in southern Helmand province, battling Taliban insurgents.
So far 222 British personnel have died in the Afghan operation.
Ten days ago Prime Minister Gordon Brown announced plans to send an extra 500 troops to Afghanistan, on condition that Kabul show a greater commitment to the effort and that NATO allies step up their contributions.
But an opinion poll released Saturday suggested falling public confidence in the mission, with 48 percent saying British troops cannot defeat the Taliban, up from 36 percent in August 2007.
Some 62 percent of respondents said they wanted troops home within a year, according to the YouGov/Channel 4 News survey of 2,042 adults on Thursday and Friday -- a figure broadly unchanged from two years ago.
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