Shrugging off the cold and wet conditions, royal fans turned out in thousands to watch Her Majesty leading a flotilla of a thousand boats to mark her 60-year reign.
Diamond Jubilee: pomp, pageantry and parties
It rained on the queen's parade yesterday. But nobody seemed to notice - not the million, flag-waving Britons lining the banks of the River Thames, nor the millions more watching on television.
In scenes unequalled since King Charles II staged his "aqua triumphalism" procession on London's river in 1652, 1,000 boats took part in the Thames Diamond Jubilee Pageant yesterday to celebrate Queen Elizabeth II's 60 years on the throne.
For 10 kilometres, the huge flotilla wound its way downstream, featuring vessels from all over the UK and Commonwealth - rowing boats, yachts, dragon boats, paddle steamers, kayaks, cruisers and even the "little ships" that helped evacuate more than 300,000 troops from the beaches of Dunkirk in the Second World War.
Historic sailing vessels and other ships too big to pass under the bridges up river, clustered around Tower Bridge in the heart of the city where the procession culminated in a swarm of boats large and small late on a damp, chilly afternoon.
But the patriotic temperature - already close to boiling point - was raised even higher as, aboard the final musical barge, the London Philharmonic Orchestra and the Royal College of Music Chamber Choir performed Land of Hope and Glory, Rule Britannia and the national anthem.
Earlier, the orchestra had serenaded the riverside crowds with Singin' in the Rain. Showers throughout the day forced a street party scheduled to be held outside the prime minister's residence in Downing Street to be moved indoors.
But, at the centre of the river pageant, was a smiling, waving Queen Elizabeth who, because of a chill wind, spent most of the two-hour journey standing behind a throne aboard the 64-metre Spirit of Chartwell, a Thames river cruiser converted into a luxurious royal barge and garlanded with almost 10,000 flowers.
At her side beneath a gold canopy was, as ever, her husband, the Duke of Edinburgh. Other royals on the barge, decorated with replica carvings and sporting a red, gold and purple colour scheme redolent of 17th century royal barges, were Prince Charles, his wife Camilla, Prince William and his wife Kate, and Prince Harry.
So many people wanted to see the event that passengers had to be turned away from stations in central England because of overcrowded, London-bound trains. At 22 locations across the country, the entire pageant was shown on giant screens in parks and public squares.
Meanwhile, more than 10,000 street parties were held across the UK and elsewhere: British explorers in the Arctic staged one as did soldiers at the British base at Camp Bastion in Afghanistan while, in New York, UK-registered yachts held their own mini-pageant along the Hudson.
The prime minister, David Cameron, who watched the Thames flotilla with wife Samantha from a moored naval vessel, praised the institution of the monarchy as a unifying force in an interview with the BBC yesterday.
Asked what the country would be like as a republic, Mr Cameron said he thought it would have less stability.
"I think one of the great things that a monarch brings - and, particularly, what a Royal Family and Her Majesty the Queen personally brings - is this sense of national unity and stability, someone who the whole country can identify with."
Several dozen antimonarchy activists who gathered near Tower Bridge for a protest meeting were booed and jeered by riverside spectators, who spontaneously broke into a chorus of God Save the Queen.