Britain's Queen Elizabeth began the fourth and final day of her Diamond Jubilee celebrations on Tuesday with a solo appearance at a thanksgiving service in St.
Paul's Cathedral ahead of a horse-drawn procession and a wave from Buckingham Palace.

People thronged the streets as the 86-year-old monarch cut a sombre figure in church, attending one of the few grand state occasions in her life without her husband of 64 years, after Prince Philip was taken ill with a bladder infection on Monday.

"The Queen will today face one of the crowning moments of her reign without the presence by her side of the man who for more than six decades has been her unfailing support," said the Times newspaper.

The 90-year-old royal consort will be kept under observation for a few days in a move the palace said was "precautionary", but takes some of the gloss of what is widely seen as a triumphant jubilee that has cemented the queen's popularity.

Millions have attended street parties and festivities, watched a spectacular 1,000-vessel pageant on the River Thames in London on Sunday and a concert in front of Buckingham Palace on Monday, all held in honour of Elizabeth II, the only British monarch other than Queen Victoria to have reigned for 60 years.

In a rare move, the queen, who usually only appears on TV screens for a short message on Christmas Day, will deliver a special broadcast be aired at 1700 GMT to thank the nation.

Crowds began massing in huge numbers on the wide Mall avenue towards Buckingham Palace, turning the famous road into a sea of red, white and blue, for the jubilee finale when the royal family will appear on the balcony, with a fly-past by modern and former Royal Air Force aircraft.     
"Some may think this is all a bit frivolous, but it's all about spreading the love," said Aba Shanti, 41, who was wearing a red, white and blue "Union Jack" flag dress.

After the celebrity glitz of the pop concert, Tuesday's events were more typical of the formal displays of ceremony for which British royalty is known across the globe.

Elizabeth - dressed in a fine silk tulle outfit, embroidered with tiny mint green star-shaped flowers embellished with silver thread - arrived at Paul's Cathedral to shouts of "God save the Queen" from crowds lining the route to St. Paul's.

A trumpet fanfare played as the monarch headed into the grand Christopher Wren-designed church, making her way up the aisle past bowing and curtsying members of the congregation.

Commentators said the church service for Elizabeth, who came to the throne aged 25 in 1952, would hold particular poignancy for the queen who as titular head of the Church of England holds her religious role close to her heart.

"We are marking today the anniversary of one historic and very public act of dedication - a dedication that has endured faithfully, calmly and generously through most of the adult lives of most of us here," said Rowan Williams, the Archbishop of Canterbury and spiritual leader of the Anglican church.

"We are marking six decades of living proof that public service is possible and that it is a place where happiness can be found," he told the congregation, which also heard a reading from Prime Minister David Cameron.

Afterwards the royals headed to receptions at two of the City of London's grandest buildings, Mansion House and the Guildhall, before a lunch at Westminster Hall, the oldest part of the Houses of Parliament.

With Philip absent, the queen will lead a horse-drawn carriage procession back to Buckingham Palace in a 1902 State Landau with heir-to-the-throne Prince Charles and his wife Camilla as military bands play and a 60-gun salute is fired.

Charles's sons Prince Harry and Prince William with his wife Kate, in an Alexander McQueen dress, will follow behind in other carriages. So far, the long weekend dedicated to the diamond jubilee has been a success story for the monarchy, their media team and Elizabeth personally.

Polls suggest the crown and the queen herself are more popular than they have been for decades, with one suggesting the hereditary monarch was considered far less out of touch with her people than Cameron and his ministers.

Meanwhile the younger generation of royals, especially William, Harry and Kate, have become the darlings of the British press, once notoriously hostile to the monarchy as it threatened to implode in the 1990s following marital infidelities and the death of Charles's hugely popular first wife, Princess Diana. - Reuters