There was a sense of deja-vu as the marchers gathered in Hyde Park, the scene of the first cannabis rally in July 1967. Some people remembered seeing Lennon and McCartney there, others, now respectable businessmen, recalled being arrested for raining flowers on police. Many of yesterday's marchers, however, had only seen archive footage on television. Caroline Coon, who set up Release in response to the arrests that day, remembered that the weather was better then.
Many things have changed in the intervening 31 years. The hippies of the '67 press reports have been replaced by modern-day crusties and eco- warriors. The equivalent of the flower children is a generation of young people newly politicised over drugs in the wake of the Criminal Justice Act, which outlawed rave parties and their repetitive rhythms. One thing, however, has not changed: the use of cannabis remains illegal, with more than 70,000 arrests for related offences in 1995. "It seems hard to imagine," Ms Coon said. "Three decades later and we're still marching for the same thing."
Hyde Park, then, where the Rolling Stones once passed a 10-foot spliff around the crowd, and the Editor of the Independent on Sunday, Rosie Boycott, rolled her first joint the same year, was full of the resonances of the past. Its message, however, was very much in the present, at its most poignant near the front of the march, where people in wheelchairs endured a gruelling two miles because in order to buy a substance which could ease the symptoms of MS, Aids and anorexia, and combat the side- effects of chemotherapy, they are forced to break the law.
"I'm a criminal," said James Thornton, a 40-year-old MS sufferer from Kent. "Cannabis eases my cramps, steadies my muscle spasms, helps me relax - but they tell me I can't buy it."
Inevitably some of the constituents of the Cannabis Campaign would be a little late, or may even turn up next Saturday. At 3pm stragglers were still arriving at Trafalgar Square. Many had brought their children; prams alongside ageing baby-boomers, young radicals and elderly smokers. One wonders whether these children will grow up to be a post-prohibition generation who will one day ask their parents: "Was dope really illegal then?" or whether in 2028, they will still be holding Decriminalise Cannabis rallies.
Walking along Piccadilly among the banners and faces painted with cannabis leaves, with the scent of marijuana heavy in the air, it seemed incredible that in 1998 people really need to march about cannabis, a part of millions of people's daily lives. But then, the march wasn't just about cannabis. A celebration of hedonism, it was also about people's freedom to enjoy themselves and how they choose to treat their own bodies in the face of illness, and how this law, above all laws, has alienated two generations of people by making them criminals.
"I'm here because my son was arrested for possession of cannabis," said one woman, who had been unsure whether to come but was having a "fantastic day out". Another woman said her daughter, now a heroin addict, had first come into contact with hard drugs through buying soft and she wanted to see the drugs separated in the market place. "I'm here because ..." a thin looking man called Toby, trailed off, suddenly quite unable to remember what he was doing in Hyde Park. "Oh yeah, cannabis," he finished eventually, to cheers from his friends from Manchester University.
As the colourful crowd wove its way along Park Lane to the beat of drums, blue-haired anarchists alongside true-blue libertarians and a sea of green balloons amid placards declaring "William Straw for Home Secretary", I thought I saw the minister's son at Reformer's Tree. It wasn't him, but it could have been because - as Mr Straw learned to his chagrin - well-educated middle-class boys also support the decriminalisation of cannabis. Had Mr Straw Jr been there, he might have appreciated his new- found hero status. Mr Straw Snr might have taken issue with the home-made posters with the face of Dawn Alford, the Mirror journalist to whom his son sold cannabis.
Allen Ginsberg, who was arrested at the '67 demonstration, and Malcolm X, who addressed the same rally, are not here to see the new campaign. Jonathan Aitken, who signed the famous '68 full-page advert in the Times in favour of the decriminalisation of cannabis, was nowhere to be seen. Nor was William Rees-Mogg, the former Times editor who wrote, at the time of Mick Jagger's arrest for cannabis possession, of the sinisterness of breaking "a butterfly on a wheel". It didn't matter. Thousands of new people have taken their place, and thousands more will take theirs, until the law is changed.