LONDON, Aug 24 (Reuters) - Flying high after their best Olympic performance in a century, Britain will celebrate the handover of the Olympic flag from Beijing on Sunday with a street party outside the gold-tipped gates of Buckingham Palace.

Some 40,000 partygoers are expected on the capital's streets for an event coinciding with the closing ceremony in China to mark the start of the countdown to the London Olympics in 2012.

The event will centre on The Mall, the ceremonial route used for royal processions, state visits and national celebrations.

Queen Elizabeth congratulated Britain's athletes and looked forward to the London Games in 2012.

"The golden triumphs of the present British team can only serve as further inspiration to those who will be working hard over the next four years to make the London Games a shining example of Olympic success," she said in a statement.

Sebastian Coe, chairman of the London organising committee and a former 1,500m Olympic gold winner, said the eyes of the world would now turn to London.

"I hope the atmosphere on the Mall and across the entire UK will be electric," he said. "It is a very proud moment for us."

Prime Minister Gordon Brown and London Mayor Boris Johnson will be in Beijing. Johnson will be handed the Olympic flag on behalf of London in a live television link-up while American swimmer star Michael Phelps will take centre stage in London.

Phelps, who won a record eight golds in Beijing, said he was sure London would rise to the occasion. "I know it's going to be absolutely amazing," he told Sky television. "I look forward to coming back here and swimming four years from now."

Britain's greatest Olympics performance for a century has thrilled the nation and reignited interest in the 2012 Games after grumbling about how much they will cost to stage.

Newspapers have devoted countless pages to coverage of Britain's beaming medal winners, under headlines like "Great Haul of China" and "Midas Britons strike gold".

On Sunday, the Royal Air Force's aerobatics team, the Red Arrows, will stage an 800mph (1,300kph) flypast over the Buckingham Palace, leaving a trail of red, white and blue smoke.

More than 400 flags will be raised across Britain, from Land's End, the most southerly point, to Unst Island, the country's northernmost island, off the Scottish coast.

Choirs will perform traditional songs in 14 cities, including "Danny Boy" in Northern Ireland. With performances in churches, libraries, museums and parks, organisers say they hope it will be the country's biggest singalong.

East London will host a 1948 street party featuring vintage clothes, afternoon tea and post-war music to remember the last time the Olympics came to the capital. Dozens of giant screens will be erected across the country for Britons to watch the handover form Beijing.