Former British Prime Minister Tony Blair has been awarded a knighthood by Queen Elizabeth II and becomes known as Sir Tony from Saturday.

Blair has been appointed as member of the Order of the Garter, England's oldest and most senior honour which is made as a personal choice of the monarch.

The ceremonial order, founded in 1348, is a recognition of significant public service, and is made without prime ministerial advice as with other New Year Honours.

"It's an immense honour," said Blair, who was the Labour Party Prime Minister for 10 years between 1997 and 2007.

"I would like to thank all those who served alongside me, in politics, public service and all parts of our society, for their dedication and commitment to our country," he said.

In other high honours conferred directly by the 95-year-old monarch, Camilla the Duchess of Cornwall - is appointed as a "royal companion".

The duchess, wife of the Queen's son and heir Prince Charles, has had an increasingly high profile with her own campaigns, including raising awareness of domestic abuse and sexual violence.

The move likely to be seen as showing the Queen's endorsement for Camilla's role as a senior member of the royal family and spouse of the future monarch.

Besides, Baroness Valerie Amos, a member of the House of Lords, becomes a "lady companion", honouring her career as international development secretary, a United Nations under-secretary for humanitarian affairs and her current role as master of University College, Oxford.

Born in Guyana, she moved to Great Britain with her family in 1963 and built a career working for equal opportunities.

A lifelong cricket fan, she is also an independent non-executive director of the England and Wales Cricket Board.

Baroness Amos, 67, and Tony Blair, 68, become two of the order's younger members, with most in their seventies, eighties and above, in a post held until death.

With the new appointments there will now be 21 "knight and lady companions" appointed by the Queen, out of the maximum of 24.

Another former British Prime Minister, Sir John Major, is among the current members of the Order of the Garter, along with businessman and philanthropist Lord Sainsbury and former MI5 chief Baroness Manningham-Buller.

These high honours are usually announced to mark St. George's Day on April 23, but the monarch chose to bring forward the appointments this year to coincide with the New Year Honours list.