This was steely performance by any standards

Jennie Bond BBC royal correspondent

Later, a crowd of around 200 gathered outside the Royal Opera House in Covent Garden, and sang Happy Birthday as the Queen Mother stood and smiled.

Wearing a pink ballgown and silver necklace, she walked unaided into the building, accompanied by the Queen.

Together with Princess Margaret - who arrived separately and was pushed into the theatre in a wheelchair - they were watching the last seasonal performance of the Royal Ballet's The Dream and A Month in the Country.

Earlier the Queen Mother greeted crowds from her buggy

Earlier in the day, thousands gathered for the festivities on The Mall, lining the route between the Queen Mother's London residence and Buckingham Palace.

Appearing for the crowds outside Clarence House, she stumbled for a moment as the Band of the Grenadier Guards marched past with a rousing rendition of Happy Birthday.

But she quickly regained her footing, and refused to use a chair provided for her.

After accepting flowers, cards and balloons from children, the Queen Mother met well-wishers in Stable Yard Road, outside the gates of Clarence House.

She then set off to meet fans in her electric buggy, painted in her light blue and gold racing colours.

People gathered there sang Happy Birthday and inquired about her health. The Queen Mother replied: "I'm feeling much better."

Salute

As well as gifts and bouquets, she even accepted a glass of champagne from the Guild of Toastmasters before returning to Clarence House.

At midday, the King's Troop, Royal Horse Artillery fired a 41-gun salute from Hyde Park to mark the birthday occasion.

Happy Birthday: Town criers entertained the crowds

Princes Charles, William and Harry then joined the Queen Mother as she reappeared at 1230BST to take the salute from the King's Troop at the gates of Clarence House.

Prince Charles' appearance had been in doubt after he fell from his horse during a polo match on Friday, and spent the night in hospital.

But he was driven away from Cheltenham General Hospital, Gloucestershire, early on Saturday, after being given the all-clear.

Princess Margaret, still suffering the effects of a stroke, was also at her mother's side in a wheelchair and wearing dark glasses to protect her eyes.

The Queen Mother, wearing a turquoise suit and matching hat and supported by walking sticks, continued to wave to the 7,500-strong crowds.

Family lunch

She was later joined by the Queen and other members of the royal family for a final public appearance before a celebratory birthday lunch.

Other royals taking part in the festivities included the Duke of Edinburgh, The Duke of York and his daughters, the princesses Beatrice and Eugenie, and Princess Anne with her husband Commodore Timothy Laurence and her children Zara and Peter.

The BBC's royal correspondent Jennie Bond said: "This was steely performance by any standards from a woman who refuses to give in to her age."

Public affection for the woman many call simply the Queen Mum has remained constant.

She became one of the symbols of British defiance in the face of bombings by Nazi Germany when she and the King refused to leave Buckingham Palace, even though it was repeatedly hit.