Musicians, actors, film-makers, artists and MPs are joining anti-war activists for a protest marking the 10th anniversary of the Afghanistan war.
The Stop The War Coalition said it is expecting a huge turnout at the event in London's Trafalgar Square to show that most Britons want a "speedy withdrawal" of UK troops.
Speakers at the so-called anti-war mass assembly will include WikiLeaks founder Julian Assange, journalist John Pilger, activist Jemima Khan, singer Billy Bragg, composer Howard Blake, musician Brian Eno, comedian Mark Steel, novelist Ahdaf Soueif, Unite union general secretary Len McCluskey, actors Simon McBurney and Mark Rylance, and a number of Labour MPs.
A Stop The War spokesman said: "After 10 years of war in Afghanistan, more than 100,000 Nato troops remain and tens of thousands have died. Government claims that the war is contributing to Britain's stability look increasingly hollow.
"Opinion polls suggest the majority of Britons want a speedy withdrawal of British troops, a view recently endorsed by the trade unions.
"Politicians have to get in step with public opinion and announce a date to bring troops home."
The demonstration will end with a march to Downing Street, led by ex-soldiers and military families.