She emerged from the gates of her official residence, Clarence House, at 11.15am wearing a sunshine yellow outfit.

The 1st Battalion of the Welsh Guards marched past with the Battalion Corps of Drums at its head, playing Happy Birthday To You.

Jenni Bond reports: "She continues to defy her age"

Admirers lining the route joined in with the serenade - some of whom had queued for days to get the best spot.

Care nurse Jennifer Hawkins, 50, from Worthing, West Sussex, had waited patiently since Saturday night.

She said: "I really can't explain too well why I love the Queen Mother so much. She's just such a lovely lady."

Royal fan Ada Brown, who was 100 years old last month, wished the Queen Mum Happy Birthday

Debbie Vallis, a 37-year-old nurse from High Wycombe, Bucks said: "I think of all the Royal Family, the Queen Mum holds her head up the highest.

"She does not seem to put a foot out of place. She seems to be a big figure behind the achievements of everyone else."

The Queen Mother seemed determined to enjoy the day to the full and ignored a chair brought forward for her by aides.

The Queen Mother used a buggy driven by her chauffeur to drive along the mall

Instead she stood and warmly greeted a procession of youngsters carrying cards, flowers and gifts,

Ten-year-old Debbie Caldicott, from Crondall, near Fleet, Hampshire, presented her with an unusual birthday gift.

She said: "I gave her an `99' ice cream for a lady who is 99 - and she laughed."

Then, followed by Minnie, one of her corgies, the birthday Royal went on a walkabout to meet some of her fans and accept hundreds of bouquets.

After strolling more than 50 metres, she boarded her now famous Queen Mum Mobile - a golf buggy in the blue and gold stripes of her horse racing colours - to ride along the banks of well-wishers.

The Guild of International Professional Toast Masters presented her with a nebuchadnezzar of champagne - containing 20 bottles - and also sang Happy Birthday.

After a marathon 55 minutes in the summer heat, the Queen Mother disappeared through the main gates of Clarence House in her buggy - with balloons tied to the back.

Family lunch

She re-emerged after a short time later, with Prince Charles and her great-grandchildren William and Harry, who drew loud screams from the teenage girls in the crowds.

Teenage girls screamed when Prince William and Prince Harry appeared with their great-grandmother

The King's Troop Royal Horse Artillery fired a 41-gun salute in Hyde Park, in honour of the occasion.

The Honourable Artillery Company also fired a royal birthday salute of 62 guns at the Tower of London.

Thirteen members of the Royal family then joined the Queen Mother for a birthday lunch, posing briefly for photographs before disappearing back into Clarence House.

They included her two daughters Queen Elizabeth and Princess Margaret, her four grandchildren Prince Charles, Prince Andrew, the newly-wed Prince Edward, Princess Anne, and several great-grandchildren.

Holiday plans

After her birthday is over, the Queen Mother is expected to travel to Balmoral for the Royals' traditional summer holiday.

The Queen and 12 other senior members of the Royal family attended a family lunch

She has been a widow since the death of her husband, King George VI, from lung cancer 47 years ago.

He was catapulted to the throne when his brother, Edward VIII, abdicated to marry American divorcee Wallis Simpson.

During the Second World War she touched the the hearts and minds of the British people when she visited bombed out areas of London and talked with victims of the Blitz.

She has earnt a special place in the public's affections through her unwavering public service, her ready smile and her fondness for parties and a bet on the horses.

Despite undergoing two hip replacement operations, there is no sign that the Queen Mother intends to retire from public engagements.