Stephen Hawking, Britain's most eminent scientist, has become the latest prominent opponent of the Iraq war by agreeing to take the lead role in a ceremonial protest to coincide with the United States presidential election.
Peace protesters will gather in Trafalgar Square at 5pm on Tuesday, where they will read out the names of 5,000 Iraqi men, women and children known to have died in the conflict.
The full death toll was put last week as high as 100,000.
Playwrights Harold Pinter and David Hare, actress Juliet Stevenson, the Mayor of London, Ken Livingstone, and relatives of British soldiers killed in action in Iraq have all agreed to take part.
Professor Hawking, the author of the best-selling book A Brief History of Time, is wheelchair-bound as a sufferer from motor neurone disease. He recorded a message on Friday that will be broadcast at the start of the rally.
The oldest protester in Trafalgar Square is likely to be a fellow scientist, the Nobel Peace Prize winner Sir Joseph Rotblat. In the 1940s, he resigned from his job developing the world's first atomic bomb on moral grounds.
Sir Joseph, who will be 96 on Thursday, said: "In this nuclear age, we simply cannot allow others to start military action unless everything else has ... been tried and has failed."
The rally comes at a time when its organisers from the Stop the War Coalition have been embroiled in controversy with one of its biggest backers, the giant public sector union Unison, which has links with the Iraqi Federation of Trade Unions, (IFTU) whose general secretary, Subhi al-Mashadani, spent more than 10 years in prison under Saddam Hussein.
Unison leaders were appalled when Mr Mashadani was barracked and jostled at a London conference two weeks ago by left-wing delegates who accused him of being a stooge for the US and British governments. The row is threatening to become an issue inside Unison, where an election is taking place for the post of general secretary - the most powerful job in the trade union movement.
Left-wing activists in the union are trying to unseat the current general secretary, Dave Prentis, for being too close to Tony Blair.
Jon Rogers, the left-wing challenger, has accused two of Mr Prentis's senior advisers, Maggie Jones and Nick Sigler, of trying to split the union from the anti-war movement. Ms Jones, who is Unison's policy director, is a former Labour Party chairman and is expected to become Labour MP for Blaenau Gwent at the next election.
Mr Sigler, who heads the union's international department, worked for many years at Labour Party headquarters.
"It is not in the best interests of Unison for circumstances to arise in which it can appear that our union is being used as a vehicle by the Labour Party leader-ship to sow division in the anti-war movement," Mr Rogers claimed in a letter to Mr Prentis, leaked to The Independent on Sunday.