Britain\'s Queen Elizabeth II sails on a royal barge down the River Thames Sunday as part of a huge pageant marking her diamond jubilee, in one of the biggest events of its kind in London\'s history. The flotilla of more than 1,000 boats is the high water mark of the national celebrations for the 86-year-old monarch\'s 60th year on the throne but the event also poses formidable security challenges. More than one million revellers are expected to watch the extravaganza of steam boats and tugs, speed boats and historic vessels in the first pageant on this scale on London\'s river since 1662. Dunkirk \"little ships\" that evacuated British forces from Europe in World War II and a Chinese dragon boat are also among the vessels accompanying the queen and other royals on the 11-kilometre (seven-mile) journey. Britons have also planned more than 9,500 street parties for Sunday. Forecasters said however that wet weather was now expected for the pageant -- which starts at 1300 GMT and is expected to last four hours -- and heavy rain hit the city overnight. A four-day national jubilee holiday began on Saturday with the queen indulging in her love of horse racing at the famed Epsom Derby horse race, where she was greeted by cheering, flag-waving crowds. Army paratroopers swooped from the sky ahead of her arrival with husband Prince Philip, 90, and other members of the royal family, who saw favourite Camelot win Britain\'s richest race. A huge red, white and blue Union flag was projected onto Buckingham Palace on Saturday night, and the huge London Eye ferris wheel on the Thames was illuminated in the national colours. The celebrations come as the royal family enjoys its highest support for decades. That is especially so for the queen, who is only the second British monarch to celebrate a diamond jubilee, after queen Victoria in 1897. The river pageant on Sunday is by far the most complex part of the festivities, and effectively doubles up as a security rehearsal for the London Olympics that open on July 27. Some 190 boats will sail alongside the pageant to handle security and respond to any emergencies, while around 5,500 police and 7,000 volunteers will be on standby. Heir to the throne Prince Charles and his wife Camilla, as well as Prince William, his wife Catherine and his brother Prince Harry, are joining the queen and Prince Philip on the sumptuous red and gold royal barge. Music ranging from the national anthem and chiming bells, to Bollywood tunes and the famous James Bond theme will blare from boats and the Thames flood barrier will be closed to ensure calm waters. A team of Australian rowers, in nine surf lifesaver boats, will be at the head of the flotilla. \"We keep being told that it\'s not a race, so we have to keep in line, and even though we will want to race each other, it\'s not a race,\" said Sarah Handley, 22, from Brisbane. Traffic will be barred from seven of the 14 London bridges that the flotilla passes beneath. On Monday there will be a concert in the shadow of Buckingham Palace featuring Paul McCartney and other top names, before the festivities culminate in the pomp and splendour of a ceremonial parade on Tuesday. There is a history of spectacular royal celebrations on the Thames including the coronation of king Henry VIII\'s wife Anne Boleyn in 1533 -- she was later beheaded -- and a pageant for King Charles II in 1662. After a rocky period including the death of princess Diana in 1997, today\'s royals are resurgent in Britain, 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. She acceded to the throne on February 6, 1952, upon the death of her father King George VI while she was away in Kenya, and was crowned the following year on June 2.