The march will be led by the Labour MP Paul Flynn, who will be joined by the founder of Italy's Radical Party, Marco Pannella, a prominent campaigner for reform of European drug laws, and MEPs from Belgium, Italy and France. Britain's most colourful cannabis campaigner, Howard Marks, is also to speak at the rally.
The police have issued a warning to motorists to avoid the Piccadilly and Park Lane area on Saturday afternoon. "We are expecting a crowd of between 5,000 and 16,000 marchers," a spokesman for the Metropolitan Police said.
One of the organisers of the last legalise-cannabis mass demonstration in London, in 1968, Caroline Coon, will be among the marchers this Saturday. "I'm tremendously excited by this development," said Ms Coon, a writer and artist and one of the founders of the drug charity Release.
"I was on the first London pot rally in 1967 and helped organise the one the following year, but I think this is going to be bigger. The drug issue is more important today than it was 30 years ago because we have all seen how the so-called war against drugs is really a war against people," she said.
During the six months that the campaign to decriminalise cannabis has been running in the IoS it has attracted the support of many prominent figures in the arts and entertainment, medicine and academia. The neurophysiologist Professor Colin Blakemore, Martin Amis, Harold Pinter, Margaret Drabble, Damien Hirst and legal expert Professor Michael Zander are among the many who have signed the paper's petition.
Join Saturday's march at Reformer's Tree in Hyde Park, central London, at midday. Information on: 0181 964 2692.