London sensationally won the right to host the 2012 Summer Olympics after beating bitter rivals Paris today in a showdown vote of the International Olympic Committee despite a last-minute appeal by President Jacques Chirac for the Games to return to France.

The UK bid beat the long-time favourites in the fourth and final round of voting at an IOC meeting in Singapore, crossing the line first with 54 votes to 50. Moscow, New York and then Madrid had been dumped out of the contest in the earlier rounds of voting.

Trafalgar Square erupted in cheers as thousands gathered there to watch the proceedings on giant television screens saw Jacques Rogge, the IOC president, open the result envelope and utter the words that seemed so unlikely only a few months ago - that the Games of the 30th Olympiad were "awarded to the city of London".

Among the special guests at the Trafalgar Square party organised by the London 2012 bid was Dame Kelly Holmes, Britain's double Olympic champion, who looked even more stunned than after her won come-from-behind victory in the Athens Olympic 1,500 metres race last year.

The victory capped a year of canny and determined campaigning by the London bid team under Sebastian Coe, the two-times Olympic champion who took over from American businesswoman Barbara Cassani in May, 2004. Lord Coe's team was also joined in Singapore by Tony Blair, who spent two days in Singapore pressing London's case with IOC members.

"It’s just the most fantastic opportunity to do everything we ever dreamed of in British sport," Lord Coe said after the result was announced. "This was the most splendid team performance. Everybody pulled together and we never lost our confidence."

The IOC decision will come as a bitter personal defeat for M Chirac, who is a former mayor of Paris, and a massive blow for the city itself, birthplace of the modern Olympic movement. The city lost to Barcelona in the contest to host the 1992 Olympics and to Beijing four years ago for the right to host the 2008 Games and its bid plans had been consistently ranked top by the IOC's own experts.

M Chirac, blamed for a potentially fatal diplomatic gaffe last weekend when he made a series of anti-British quips on a visit to Russia, heard the news in mid-air, having left Singapore after the final Paris sales pitch for the G8 summit at Gleneagles, hosted by Mr Blair.

In a statement from his office, M Chirac congratulated London and wished Britain "good luck" in organising the Games. Mr Blair, already ensconced behind the G8 security barrier at Gleneagles, said: "It is a momentous day for London... It is fantastic. I am thrilled."

London's sporting ambassadors in Singapore appeared more shocked than anyone. David Beckham, the England football captain who was born and bred in the area where the Games will be centred, broke into tears at the Raffles Plaza auditorium. Alongside him, stunned by one of the biggest upsets in Olympic history, were Lord Coe, Sir Steve Redgrave and Sir Bobby Charlton.

Also in Singapore was Tessa Jowell, the Culture Secretary. Downing Street said today that Ms Jowell has also been appointed Minister for the Olympics, ensuring the presence in Cabinet of a politician with direct responsibility for the Games.

Sir Matthew Pinsent, the rower, compared the margin of victory to that in his own final Olympic victory. "It was four votes between winning and losing -- as close as our race in Athens," he said.