The Queen’s Jubilee celebrations are to conclude with a glittering procession and service of thanksgiving at St Paul’s Cathedral.
Prince Philip is still in hospital with a bladder infection and will miss the final events marking the Queen’s 60-year reign.
A service at St Paul’s Cathedral will be followed by a carriage procession and, weather allowing, an RAF flypast.
Queen Elizabeth II recorded a message of thanks to the nation ahead of a star-studded concert at Buckingham Palace on Monday.
The two-minute message, filmed in her private apartments at the palace, will be broadcast at 18:00 BST on radio and television in the UK and across the Commonwealth.
Crowds have started building up outside St Paul’s and Buckingham Palace, which the Queen will leave at 10:15 BST in her state Bentley for the service.
The fourth day of celebrations will be a more formal affair, with the Archbishop of Canterbury, Dr. Rowan Williams, giving a sermon in front of the Royal Family and leading national figures.
Prime Minister David Cameron will lead the large representation from the government at St Paul’s alongside diplomats and foreign leaders.
After the service, the Queen will attend a reception at Mansion House – the official residence of the Lord Mayor of London. The Prince of Wales and Duchess of Cornwall will attend a similar event at the Guildhall.
A City of London Livery companies lunch at Westminster Hall will follow, after which the royals will take part in a carriage procession through Whitehall.
Guests will dine on salmon, followed by Welsh lamb, grilled Isle of Wight asparagus, Jersey Royal potatoes and chocolate delice, bread and butter pudding and berry compote with apple sauce.
Personnel from all three armed services will line the streets for the procession, and the King’s Troop will fire a 60-gun salute.
As the royals arrive back in the forecourt of Buckingham Palace, there will be a guard of honor. They will then gather on the balcony to watch a fly-past of World War II aircraft and a display by the Red Arrows.
Prince Charles, the Duchess of Cornwall, the Duke and Duchess of Cambridge, and Prince Harry are among the royal family members involved in the events.
Forecasters say the weather in central London will be cloudy and dry at first, with a top temperature of 14C, but there may be outbreaks of rain in the afternoon.
Prince Philip, 90, will remain under observation at King Edward VII Hospital in London, where he was taken on Monday as a “precautionary measure”.
In December, he was treated at Papworth Hospital in Cambridge for a blocked coronary artery.
At the concert on Monday night, attended by 12,000 people, Prince Charles paid tribute to his mother, describing her as “mummy” and a “very special person”.
But he added there was a disappointing edge to the night.
“The only sad thing about this evening is that my father couldn’t be with us because, unfortunately, he was taken ill,” Prince Charles said.
Take That star Gary Barlow, who helped organize much of the concert and sang a duet with Cheryl Cole, said the prince’s illness was “sad, really sad”.
Robbie Williams opened the show with Let Me Entertain You and was the first to perform for the Queen when he sang big band classic Mack the Knife. Other performers included Kylie Minogue, Jessie J, Annie Lennox, Sir Tom Jones, Madness, Stevie Wonder and Sir Cliff Richard – singing a medley of his songs from six different decades.
The concert was brought to a close by Sir Paul McCartney who played hits including Magical Mystery Tour, Let It Be and a rendition of Live and Let Die, complete with fireworks and pyrotechnics.
After the show, the Queen pressed a diamond-shaped crystal into a pod, igniting a beacon in The Mall to mark her 60 years on the throne. It was one of more than 4,000 lit across the UK and the Commonwealth.