The march was headed by a number of demonstrators dressed as occupation troops who pretended to torture other protesters wearing black hoods, in scenes reminiscent of photographs of the torture of Iraqi prisoners by US soldiers. Others dressed up as gun-toting British soldiers.
The activists, who also called for British Prime Minister Tony Blair to resign, were watched by a strong contingent of police as they began walking alongside the River Thames in central London.
"We are protesting about the shocking abuses in Iraq and call for the withdrawal of the illegal aggressor forces," said Kate Hudson, a spokeswoman for the Campaign for Nuclear Disarmament.
The protest, organised by the Campaign for Nuclear Disarmament, the Stop the War Coalition and the Muslim Association of Britain, ended with a rally in Trafalgar Square, where London Mayor Ken Livingstone addressed the crowd.
"There is nothing more to say than that the only way to end these horrors is by bringing our troops out of Iraq immediately," said Livingstone, a member of Prime Minister Tony Blair's Labour Party.
Referring to US presidential elections later this year, Livingstone said he hoped President George Bush would be "consigned to the dustbin of history in November."
Resigned member of the House of Commons, George Galloway, who also attended the demonstration, referred to Bush and Blair as "torturers".
"They said they would bring democracy but they brought savage dags and chains. They said they will bring human rights, but they are actually bringing sexual degradation and torture," he told Aljazeera
The Stop the War Coalition is best known for a million-strong demonstration through London's streets in February 2003 against the US-led invasion of Iraq that came the following month.