Up to 40,000 people enjoyed the Visa London 2012 Party on the Mall with a host of top acts including Heather Small, The Feeling, Katherine Jenkins and Il Divo performing Games-inspired songs.
Beijing Olympic medallists Michael Phelps, Bradley Wiggins and Phillips Idowu were among those also on stage to celebrate.
The Handover Ceremony in Beijing and party on the Mall was broadcast live on
giant screens in more than 30 locations around the UK. 20,000 people in Cardiff, 15,000 in Weymouth, 6,000 in Glasgow, 30,000 in Liverpool, and 10,000 in Belfast were among those getting together to watch. Millions more tuned in on BBC One and Radio 2.
In a first in the history of the Games, special
Handover Flags were proudly raised at over 600 sites around the UK and internationally, from Lands End to John O'Groats and in symbolic spots such as the highest mountain in England, Scafell Pike, Stonehenge and the Paddiwack Yacht in the Isle of Wight.
Other events included sports and culture displays, from a carnival in Coventry to 'Sing the Nation' events.
Sir Keith Mills, Deputy Chairman of the London 2012 Organising Committee said: 'The eyes of the world have been on Beijing for the last two weeks as they have staged one of the most spectacular and uplifting Olympic Games ever and for that we congratulate them. For a short amount of time today however, the world stopped and considered what's coming next.
'We welcomed them, showed our enthusiasm and as a nation uplifted by the most successful Team GB performance in 100 years we were united in celebration.
'Today was a truly historic day and London 2012 would like to thank the communities who joined in the celebrations at Live Sites and to the 400 venues up and down the country who raised a Handover Flag and showed their support as we take the first step on this magnificent, challenging and momentous journey to the London Olympic Games in 2012.'
Read the full media releaseRead an account of the day including what the performers and athletes at the Visa London 2012 party had to say about the show and the Games coming to London.
Read more about the Handover in Beijing