London's dream of hosting the 2012 Olympic Games became a reality today.

The capital won a sensational victory against the odds when the final votes of International Olympic Committee delegates in Singapore were counted.

London beat Paris to the prize after months of determined campaigning which went right down to the wire.

The British and French capitals made it to the fourth and final round of voting after first Moscow, then New York and Madrid were eliminated in earlier rounds.

And London managed to attract enough support from delegates to beat firm favourite Paris in the run-off.

Joy erupted in Trafalgar Square and east London as sports fans heard the news. Organisers of the two bids had faced an agonising hour-long wait before the final decision was officially announced by IOC president Jacques Rogge.

The whole voting process took less than half an hour but Mr Rogge stuck to the official timetable, revealing the result shortly after 12.45pm UK time.

London's bid organisers surged ahead after a slick and forceful final presentation earlier today.

Bid leader Lord Coe promised a Games where "magic happens" if delegates handed the UK capital the Olympic torch.

Lord Coe, the London 2012 bid chairman and a double Olympic champion, said the capital was offering a "vision of inspiration and legacy" for future generations.

Tony Blair recorded a message for the presentation in which he highlighted South African President Nelson Mandela's support for the London bid.

The Princess Royal, speaking in her role as an IOC member and as a board member of London's bid, began London's crucial final presentation with a message of support from the Queen.

And it appeared to do the trick as London beat the bid from Paris - the third by the French capital in recent years.

The victory means that London will play host to the world's premier sporting event in seven years' time with a specially-built stadium and village rising from what is now an urban wasteland in the east of the city.

Mayor of London Ken Livingstone said: "This is one of the best days London has ever had - and it is one of the proudest days for Britain and for British sport. We had the confidence to go for it and we have won the greatest prize in sport.

"When we began this bidding process very few people believed that we could win but London's renaissance has overcome all the obstacles.

"It has been a gruelling but great competition against five world cities who all put together excellent bids all truly worthy of the Olympic movement and ideals."

He added: "I would also like to thank everyone involved in the monumental effort they have put into creating London's world beating bid.

"Londoners themselves deserve thanks for the tremendous support they have shown for our bid. Without public support we could not have won.

"The IOC have given us an extraordinary opportunity which we must now live up to.

"In 2012 we will repay this honour by staging the greatest Olympics and Paralympics ever and show the world what London and Britain can do."

Prince William, who is on a tour of New Zealand, said: "I'm absolutely delighted that London has won the 2012 bid and I'm looking forward to what I'm sure will be a fantastic Olympic Games."

Sussex will receive spin-off benefits from the IOC's decision to award the Olympic Games 2012 to London.

Crawley's K2 sports centre, which opens later this year with the only 50m swimming pool in the South outside London, an athletics track and indoor gymnastics hall, could be used.

Other facilities in line to be used, if only for practice, include the projectile hall for shooting in Worthing, which is one of a handful in the country, the water-based hockey pitch in East Grinstead and Eastbourne's international tennis venue at Devonshire Park.

The All England Jumping Course in Hickstead is not expecting to be involved, having already been told by the London bid team there are no plans to incorporate it in the project.

Chris Carter, Brighton and Hove Athletics Club chairman, said: "It's tremendous because it's a great motivation for our athletes and the permanent sites for the Olympics will remain for future generations.

"There will be more investment in sport over the next seven years and, with the Olympics being in London, this will be felt in the South-East."

Double Olympic gold rowing champion James Cracknell visited Chesswood Middle School, Worthing, yesterday as part of an initiative to get youngsters exercising regularly.

He said: "Sport is going to be in the headlines for the next seven years, inspiring people to take it up."

Wade Bennett-Jackson, 18, from Worthing, Britain's sprint hopeful, is looking forward to competing in London as the world's number one.

He said: "The facilities will be really good before and after the Olympics, getting everyone involved in sport and helping them fulfil their potential."

Plans for Brighton and Hove to be part of year-long celebrations preceding the 2012 Games are already under way.

A Brighton and Hove City Council spokesman said: "It's fantastic news for the city. We're known throughout the world as a cultural centre and a place to have a good time so we believe we'll be strongly placed to benefit from the extra tourism the Olympics will undoubtedly generate.

"We'll also be exploring the possibility of enabling teams to set up training camps using the city's sporting facilities, which will hopefully by then include a community stadium at Falmer."

Councillor Ian Lucas, Eastbourne Borough Council leader, said: "This is fantastic news for the UK and for Sussex. We'll be reaffirming our offer of assistance in providing training facilities and accommodation in Eastbourne, which holds one of the largest accommodation stocks in the South-East."

Councillor Robbie Sharma, Crawley Borough Council's executive member for leisure and culture, said it was an opportunity to improve sporting facilities, encourage youngsters into sport and give the country something to be proud of.

He said: "Crawley's proximity to London and excellent facilities mean 2012 could bring some exciting opportunities to the town."