Britain's Prince Harry, Megan, Duchess of Sussex, and Lady Sarah Chatto attend the National Service of Thanksgiving held at St Paul's Cathedral, during Britain's Queen Elizabeth's Platinum Jubilee celebrations, in London, Britain, June 3, 2022. Victoria J
Britain's Prince Harry, Megan, Duchess of Sussex, and Lady Sarah Chatto attend the National Service of Thanksgiving held at St Paul's Cathedral, during Britain's Queen Elizabeth's Platinum Jubilee celebrations, in London, Britain, June 3, 2022. Victoria Jones/Pool via REUTERS. Reuters / POOL

Tens of thousands of people flocked to Buckingham Palace to celebrate Queen Elizabeth's Platinum Jubilee on Saturday and watch a pop concert that started with the 96-year-old monarch having tea with Paddington Bear.

In a short video, the queen revealed that she kept the Bear's favourite - a marmalade sandwich - inside her ever-present handbag. She then started tapping along to the tune of the Queen rock anthem "We Will Rock You", which opened the show.

A host of performers will appear on stage, including Alicia Keys, Diana Ross and Rod Stewart, before the queen's son and heir Prince Charles, and her grandson Prince William, pay tribute to the record-breaking monarch following her 70 years on the throne.

By early evening, tens of thousands of people had gathered on the Mall, the grand boulevard that runs up to the palace, and in a nearby park to watch the concert on big screens, while those with tickets surrounded the stage on a warm evening.

The opening video between the queen and the fictional character from children's literature had echoes of 2012 when she appeared with Britain's most famous fictional spy James Bond in a video for the opening ceremony of the London Olympics.

The monarch was not present at Saturday's concert due to the "episodic mobility problems" that have caused her to cancel a number of engagements recently.

Andrew Singleton, a 56-year-old window fitter from northern England who was in the queue for the concert, said the Jubilee had helped to bring the country together.

"People have travelled from as far as America to actually come here and just enjoy the celebrations," he said.

Earlier in the day the queen also missed the Epsom Derby horse race.

Her daughter Princess Anne, who competed in the three-day equestrian event in the 1976 Olympics, stood in for her mother, who has rarely missed the race during her record-breaking reign and watched on television from her Windsor Castle home.

LILIBET'S BIRTHDAY

Four days of celebrations to mark the monarch's 70 years on the throne began with a military parade, a Royal Air Force flypast, and the lighting of beacons across Britain and the world, with tens of thousands of people joining the festivities.

A sideshow to the main celebrations has been Prince Harry and his American wife Meghan making their first public appearance together in Britain since quitting official duties to move to Los Angeles two years ago, during which time their relationship with other royals has become strained.

Notably on Saturday, the official Twitter accounts for the monarch, Charles and William all sent messages almost simultaneously to mark the first birthday of Lilibet, the couple's daughter who is named after the queen.

Elizabeth had not met her great-granddaughter prior to the trip, and Buckingham Palace has not commented on newspaper reports they had now finally been introduced.

Harry and Meghan have become divisive figures, with supporters regarding them as a breath of fresh air for the tradition-bound monarchy, while critics and many newspapers pour scorn on their commercial activities such as striking a deal with global streaming service Netflix.

"So Far Apart", the Daily Mail newspaper said on its front page about the lack of any obvious interaction between Harry and elder brother William at Friday's thanksgiving service.