Hundreds of thousands of people have lined the streets of the capital to watch the New Year's Day Parade celebrating the start of the Olympic year.
More than 8,000 performers, including US marching bands, cheerleaders and dancers took part in the 26th annual event.
The three-hour spectacular celebrates the start of a year which includes the Queen's Diamond Jubilee and the Olympic Games.
It began at noon at the Ritz Hotel and followed a 2.2-mile route through Piccadilly Circus, Trafalgar Square and Whitehall before ending at Parliament Square in front of Big Ben. The Jacksonville State University Marching Southerners, from Alabama, kicked off the procession, followed swiftly by All The Queen's Horses.
Dan Kirkby, communications director of London's New Year's Day Parade, said: "The 26th New Year's Day Parade here in London is a wonderful platform for a fantastic city. The first day of 2012, a legendary year for London, and we have got 8,500 performers from all over the world, 19 London boroughs represented, half a million people out on the streets. It's a fantastic day."
However, the parade's grand finale was scrapped because of heavy rain, organisers said. Four of the marching bands, who performed earlier in the procession, were due to perform together to close the 2012 parade.
Mr Kirkby said: "We are cutting short our grand finale because it is a deluge here. It's absolutely pouring out of the skies. All four marching bands have performed already but we were going to bring them all together as one mass band with about 800 people.
"It's disappointing we have had bad luck with the weather but at least we got over half way through the parade before the heavens opened."
The Queen, who will become only the second British sovereign to reign for 60 years when she celebrates her Diamond Jubilee later this year, had a new year's message printed in the free guide given to spectators.
She said: "Please convey my sincere thanks to everyone who is involved in the London New Year's Parade this year, for their kind message of loyal greetings. I was pleased to learn that the theme chosen for this year's parade will be the Diamond Jubilee and I send my warm good wishes to the instrumentalists, choirs and indeed to all the performers who will be taking part in the occasion. I am sure that it will be a wonderful event."