Snow fell across London today before an Olympic torch relay through the capital that is expected to attract anti-China protests.

About 80 athletes and celebrities will carry the torch by foot, bike, boat and bus during a 50-kilometre journey starting at Wembley Stadium and ending in Greenwich.

The 2008 Games take place in Beijing from August 8 to 24. The next Summer Olympics are in London in 2012.

Anti-China protesters are set to appear at key points along the route. Police have said they will be dealt with firmly if they try to disrupt the torch's journey.

The event has drawn "substantial" interest from groups who plan to stage protests against China's human rights record and its crackdown on independence campaigners in Tibet, Scotland Yard has said.

Police have been notified of at least six protests, including one outside Downing Street where Prime Minister Gordon Brown is due to greet the flame, carried by a local schoolboy.

About 2,000 police officers will be on duty during the day, including some on bicycles to keep up with the torch.

Organisers will be hoping no more torchbearers drop out of the event after a handful withdrew in the run-up to today.

The BBC's deputy director general Mark Byford backed out due to concerns his participation would compromise the corporation's journalistic standards.

China's ambassador to London, Fu Ying, was expected to take part despite concern she would act as a focal point of protests.

Tens of thousands of spectators are expected to line the route.

Among those they will be cheering on will be tennis player Tim Henman, girl band Sugababes, actress Denise van Outen, news presenter Trevor McDonald, violinist Vanessa Mae, yachtswoman Ellen MacArthur and Arsenal footballer Theo Walcott.

Former rower Steve Redgrave, who won gold medals at five consecutive Olympics, will start the relay and it will end when the flame is handed to middle distance athlete Kelly Holmes, who won two gold medals at the 2004 Games.

The Olympic torch arrived yesterday evening from St Petersburg, Russia, and heads to Paris after London.

The route will take in 21 international cities and every Chinese province before the Beijing Games open.