The Olympic Flame will arrive in the UK on Friday night after it was handed over at a ceremony in Athens.
British delegates including David Beckham fly back from Greece to RNAS Culdrose in Cornwall.
They will attend a special ceremony welcoming the flame, before it is taken on a 70-day relay involving 8,000 torchbearers covering 8,000 miles.
The flame will finally reach east London's Olympic Stadium and the opening of the Games on July 27.
London was officially handed the flame yesterday in a rain-hit sundown ceremony at the old Panathenaic Stadium, venue of the first modern Olympics in 1896.
The flame was handed over to London to host the Games for the third time since the birth of the Olympics - in 1908, 1948 and now 2012. No other city has staged the Games three times.
Despite the buzz triggered by the last-minute news that LA Galaxy star and former England skipper Beckham was flying in specially to be part of the ancient ceremony, the more formal duties came down to the Princess Royal.
Both she and Karolos Papoulias, the Greek president, sat in ancient thrones that are part of the stadium during the hour-long event.
The flame was handed to the Princess, who was watched closely by other members of the official delegation including London 2012 chairman Lord Coe, Olympics minister Hugh Robertson, London mayor Boris Johnson, Beckham and five British sporting teenagers.
In his speech, Lord Coe thanked the damp crowd for Greece's warm hospitality and also for "laying on the British weather for us".
The past week had linked Britain and Greece in a "very special way in the spirit of peace and friendship", he said.
He added that the arrival of the flame on British shores will be a "resounding clarion call" to the world's top athletes to gather for the Games, and millions of Britons have been working hard to create a great welcome.
"If the Olympic Games are about celebrating the best athletes in the world, the Olympic spirit is about celebrating the best in ourselves and in our communities.
"We have found the very best torchbearers who, like Olympic athletes, will inspire a generation.
"As we prepare to bring the flame to the UK, we are reminded of our responsibility - like that of our predecessors in 1908 and especially 1948 - to stage Games that use the power of sport to unite the world in a celebration of achievement and inspiration in challenging times. A Games that will inspire the next generation to choose sport," he said.
Each member of the British delegation sheltered under blue umbrellas as they walked through the centre of the stadium to their front-row seats.
Everyone from the Princess Royal to Mr Robertson was named over the loudspeakers and greeted by cheers from the crowd.
There was also a chuckle from British people in the crowd as the announcer introduced Beckham as "Sir David".
The youngsters, who were picked by London 2012 for displaying Olympic values, exchanged symbolic olive branches to the tune of John Lennon's Imagine.
The five, who come from different UK regions, were from schools and colleges which are part of London 2012's Get Set education network and school linking programmes run by the British Council.
A smiling Sakinah Muhammad, 15, from Clapton Girls' Academy in Hackney, east London, said: "When I first found out, I was in shock. I did not believe what they were telling me and that I was going to be something that is such a big deal."
The other British teenagers included Scottish rugby player Dennis Coles, 17, from Doon Academy, Dalmellington, East Ayrshire; hockey player Chloe Brown, 18, from South Eastern Regional College in Bangor, Northern Ireland; and Swansea Harriers athlete and Mumbles Rangers FC player Sean White, 17, from Bishop Vaughan Catholic School in Swansea.
There was also Georgia Higgs from Helston Community College, a Falmouth Ladies hockey player and school sports ambassador who represents Cornwall.
The Olympic Flame was taken on a relay around the Greek mainland and islands since it was lit by the rays of the sun in ancient Olympia last week, before a trio of world champions brought it safely to the stadium.
It arrived in the hands of rower Christina Giazitzidou and was then carried by gymnast Vasilis Tsolakidis and rower Alexandra Tsiavou.
Chinese gymnast Li Ning, who lit the cauldron at the opening ceremony for the 2008 Beijing Games, and Greek weightlifter Pyrros Dimas were the last torchbearers in Greece.
In a symbolic move by the Hellenic Olympic Committee, they were picked to represent a link between the last Olympics in Beijing, Greece as the birthplace of the institution, and the next Games in London.