London: Britain on Saturday kicks off four days of celebrations to mark Queen Elizabeth II's diamond jubilee, including a 1,000-boat river pageant and a star-studded concert.

The queen starts the festivities by indulging in her love of horse racing at the Epsom Derby on Saturday before riding in a ceremonial barge on the Thames at the centre of the giant flotilla on Sunday.

One million people are expected to line the river to see the extravaganza of steam boats and tugs, speed boats and historic vessels.

A concert in the shadow of Buckingham Palace featuring Paul McCartney and other top names is the highlight on Monday before the four-day extravaganza culminates in the pomp and splendour of a ceremonial parade on Tuesday.

Aside from the setpiece events in London, millions of people up and down the country are commemorating the jubilee by throwing a party at home.

"It looks like the entirety of Britain is going to turn out," said historian Kate Williams, the author of "Young Elizabeth: The Making of our Queen".

They will be making the most of the two-day public holiday granted for an historic occasion -- the queen is only the second British monarch to celebrate a diamond jubilee, after queen Victoria, in 1897.

Union Jacks are fluttering in streets and shop windows and retailers report that red, white and blue bunting and even jubilee garden gnomes are selling fast.

The celebrations take place as the royal family enjoys its highest support for decades, with a recent poll showing that 80 percent of Britons want the country to remain a monarchy.

Those levels of support are comparable to 1953, the year of the queen's coronation.

Coming hot on the heels of Prince William's wedding to the then Kate Middleton last year, the jubilee is likely to further boost the royals' popularity.

Amid the acclaim for the queen it is easy to forget that just a decade ago, the picture was very different.

Following the death of Diana, princess of Wales, in a Paris car crash in 1997, the monarch was widely criticised for failing to join in the public outpouring of grief.

She did eventually bow to Diana's coffin as it passed, a moment that Williams says was a turning point.

Now there is a "massive surge" of affection for the queen both in Britain and across the Commonwealth, said Williams.

"At the moment the queen's popularity is as high as it's ever been since her coronation," she said.

"This is really quite incredible when you think about how extraordinarily unpopular she was after the death of Diana."

At the centre of the celebrations is an 86-year-old great-grandmother, who was visiting Kenya in February 1952 when she was told that her father, King George VI, had died at the age of 56, thrusting her into the role of queen.

(Agencies)

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