Derby Day marks the start of Diamond Jubilee celebrations
The Queen has watched the Derby at Epsom, having earlier driven on the race course to begin the first major event of the Diamond Jubilee weekend marking 60 years of her reign.
Racegoers cheered as the royal motorcade arrived at the winning post. Mezzo-soprano Katherine Jenkins then sang the national anthem.
Meanwhile, gun salutes echoed across London, Edinburgh, Cardiff and Belfast.
Street parties were held in numerous locations, with more planned later.
The Queen, wearing royal blue, was accompanied by the Duke of Edinburgh along with their sons the Duke of York and Earl of Wessex, and granddaughters Beatrice and Eugenie.
After some time in the royal box, she went to the paddock to inspect some of the horses running in the Diamond Jubilee Coronation Cup.
After the race she awarded the cup to Aidan O'Brien, the trainer of the winner St Nicholas Abbey, as well as meeting the horse's owner and jockey.
About 130,000 people were estimated to be at Epsom, according to Surrey Police.
The favourite Camelot won the Derby, giving Aidan O'Brien his fourth straight Classic winner, following victory for his horse Was in the Epsom Oaks on Friday, and Camelot's 2,000 Guineas win and the triumph of Homecoming Queen in the 1,000 Guineas at Newmarket in May.
Singer Jenkins said of her performance: "I don't think I've ever actually sung the anthem just as close. I mean, she was literally a few feet away from me. So this is definitely a day that I will never forget."
Meanwhile, crews of a 1,000-strong flotilla have been putting finishing touches to their vessels in preparation for their role in escorting the royal barge along the Thames on Sunday for the Jubilee flotilla.
One skipper, Rob Salvidge from Ramsgate, said the excitement among his fellow sailors was building.
"Tomorrow this river is just going to be full of a who's who, really, of all sorts of interesting ships - great and small, old and new - from the history of Britain and also the history of the monarchy... celebrating the Jubilee."
Among other items of Jubilee news:
- Up to 6,000 extra police officers will be on duty throughout the events and celebrations in London
- A campaign to rename the tower housing Big Ben for the Queen has received the backing of the majority of MPs
- Traffic heading for Dover ferry port came to a standstill for a time as eight-mile queues built up as part of the bank holiday getaway
- Seven thousand security stewards will be on the banks of the Thames during Sunday's flotilla
- More than 300 applications have been made to close roads for street parties in Wales
- Hillsborough Castle has been the focal point for celebrations in Northern Ireland, with a 21-gun salute, fly-past and medal ceremony
- Thousands of Jubilee revellers attended London's Hyde Park for the first of the two-day Jubilee Family Festival
- The crowds saw scenes from West End shows Billy Elliot the Musical, The Lion King and War Horse. There were also appearances from some of the BBC's Strictly Come Dancing stars including Chelsee Healey and Robbie Savage
Light rain fell in some parts on Saturday, while Sunday's river pageant could be doused in rain with temperatures reaching a high of 11C, according to BBC Weather.
The weather forecast is poor for the official celebrations and street parties in the south of England, while the north of England and Scotland are the most likely areas to avoid the rain.
Millions of Britons are expected to take part in Jubilee parties, outdoor concerts and fairs being staged across the country over the weekend.
On Sunday, in what is being called the Big Jubilee Lunch, people all over the UK are being encouraged to share lunch with neighbours and friends in street parties or picnics to bring communities together.
On Monday, a concert will be held in front of Buckingham Palace in the area surrounding the Queen Victoria Memorial, with performances from artists including Dame Shirley Bassey, Sir Elton John, Jessie J, JLS and Ed Sheeran.
When it ends at 22:00 BST, more than 4,000 beacons are due to be lit in the UK and around the world.
Some 200 beacons will be lit in Wales to mark the occasion. First Minister Carwyn Jones paid tribute to the Queen, saying: "It is right to say that this is a truly historic occasion, and I get a real sense that across Wales it is being embraced by people from all walks of life and different communities."
The Queen will light the UK's last beacon - the National Beacon - at about 22:30 BST, to be followed by a firework display at Buckingham Palace.