Great Britain's Olympic and Paralympic stars have been honoured with a parade through central London.
The procession to celebrate their efforts in Athens included 47 Olympic medallists and 37 Paralympic athletes.
Double gold-medallist Kelly Holmes said: "This is amazing. I could never have imagined the response I got."
The Olympic athletes then moved on to Buckingham Palace for a special reception hosted by The Queen and other senior members of the Royal Family.
Prince Philip, the Princess Royal, Prince Andrew and Prince Edward were all in attendance as medal winners were taken into the palace's White Drawing Room before mingling with their fellow athletes and team support staff.
Several medallists - including Leslie Law, Pippa Funnell and William
Fox-Pitt - who had their positions upgraded after various controversies at Athens, received their medals from Princess Anne at an award ceremony in the Palace Ballroom.
After leaving the reception, boxing silver medallist Amir Khan said: "It's an honour to be here, especially seeing the Queen for the first time.
And sprinter Jason Gardner, part of the victorious 4x100m men's relay team, added: "I don't think it gets any better to be invited to Buckingham Palace and to meet the Queen personally, especially with my team-mates."
The Paralympic athletes will go to the palace for a separate reception at a later date.
The office of London's mayor said that an estimated 15-20,000 had gathered in Trafalgar Square, where a reception was held for the athletes.
The crowds were smaller than expected - and a fraction of the estimated 750,000 who turned out to cheer on the World Cup-winning rugby union team last December.
But a BOA spokesman said: "It's fantastic that people turned out in the droves that they did today, hundreds of thousands of people to cheer them on and celebrate their achievements."
And the athletes insisted they were delighted by the turn-out.
"I'm amazed so many people have come out. It's very humbling," said Ed Coode, part of Britain's gold-medal winning coxless fours in Athens.
Gail Emms, who partnered Nathan Robertson to badminton silver, added: "It's been fantastic.
"It's an experience I will never forget. The public really got behind us in Athens and that really helped us get to the final - so we just want to thank everyone."
With London still in the running to stage the 2012 Olympic and Paralympic Games, it is hoped the celebrations will help foster more support for the bid.
"The day is very much about 2004 and celebrating the huge successes of both the Olympic and Paralympic teams in Athens," said Simon Clegg, chief executive of the British Olympic Association.
"But of course it will send a very important message to the international sporting community that we love celebrating sporting success in this country."
There had been criticism of the timing of the parade, which came nearly two months after the Olympics and a week before school half-term when many more children would have been able to attend.
However, though the crowds were slow to build, thousands of people saw the five floats travel through Piccadilly Circus, the Haymarket and Pall Mall, ending in Trafalgar Square.
Team GB returned home from the Olympics with 30 medals - nine of them gold.
It was the best medal haul by Britain since the 1984 Los Angeles Games which were boycotted by the Eastern Bloc.
Monday's parade also provided the first chance to revel in the success of Britain's Paralympic stars.
In September, the British Paralympic squad also came back from Greece with plenty to show for their endeavours.
Britain climbed to second place in the overall medal table behind China, with a haul of 94 medals, including 35 golds.
Double gold medallist Tanni Grey Thompson became Britain's most successful Paralympian in Athens after taking her after tally to 11.
However, the Welsh athlete did not take part in Monday's parade because she is involved in a fundraising event for children in India.