Queen Elizabeth II is due to attend a public service of thanksgiving at St Paul's Cathedral in honor of her 80th birthday, joined by British Prime Minister Tony Blair and other dignitaries.

In another grand ceremonial event since she turned 80 on April 21, the queen and members of her family will see 2,300 guests gather in the historic cathedral in the heart of London.

Queen Elizabeth II greets well-wishers during a walkabout. The Queen is due to attend a public service of thanksgiving at St Paul's Cathedral in honor of her 80th birthday, joined by British Prime Minister Tony Blair and other dignitaries. [AFP]

On hand will be her consort and husband Prince Philip, her eldest son and heir-to-the-throne Prince Charles as well as his two sons, Princes William and Harry, and other royals.

The Queen's Bodyguard, the Yeomen of the Guard, in their red and gold uniforms, will also take up position in the cathedral.

Blair, who is expected to be accompanied by his wife Cherie, is due to be accompanied by senior members of the cabinet, according to Buckingham Palace, the queen's residence in London.

Among the 2,300 guests will be military chiefs, multi-faith leaders and opposition politicians, including Conservative Party leader David Cameron and Liberal Democrat leader Sir Menzies Campbell.

Security is expected to be tight.

Archbishop of Canterbury Rowan Williams, the spiritual leader of the world's Anglicans, will deliver the sermon at St Paul's.

"As we mark the year of her 80th birthday, we give thanks for steadfast commitment to the calling that is hers, freely given to this nation and Commonwealth," according to excerpts of the sermon.

Elgar's "Pomp and Circumstance" will be among the music which will stir in the historic setting, and the hymns include "Praise My Soul The King Of Heaven" and "All People That On Earth Do Dwell."

The service will end with the national anthem.

One hundred members of the public who were picked from a ballot will also be seated in the cathedral after being selected from those who wrote to the palace asking for tickets.

The queen and Prince Philip, who just turned 85, will later wander outside the cathedral to greet well-wishers.

She will attend a special birthday lunch for more than 350 VIPs at Mansion House hosted by the Lord Mayor and the Corporation of London.

The queen will deliver a short speech, followed by words from the prime minister.

Some 15,000 people flocked to Windsor Castle, the ancient royal retreat west of London, to celebrate her birthday on April 21.

The celebrations highlighted how her popularity has endured despite the family divorces and scandals that shook the House of Windsor in the 1990s and raised doubts about how long the monarchy would last.