Half a million people have signed a petition to have former prime minister Tony Blair’s knighthood “rescinded”.

Sir Tony is appointed by the Queen a Knight Companion of the Most Noble Order of the Garter, the oldest and most senior British Order of Chivalry.

The Change.org petition, set up three days ago, which aims to strip the former Labour leader of his appointment, reached 500,000 signatures on Monday.

A statement on the website said: “Tony Blair caused irreparable damage to both the constitution of the United Kingdom and to the very fabric of the nation’s society.

“He was personally responsible for causing the death of countless innocent, civilian lives and servicemen in various conflicts. For this alone he should be held accountable for war crimes.

“Tony Blair is the least deserving person of any public honour, particularly anything awarded by Her Majesty the Queen.

“We petition the Prime Minister to petition Her Majesty to have this honour removed.”

Sir Tony, 68, led New Labour to a landslide victory in 1997, winning two subsequent general elections before quitting Westminster a decade later, paving the way for his chancellor Gordon Brown to take over as prime minister.

He was prime minister during the Allied military invasions of Iraq and Afghanistan.

The former barrister became a Middle East envoy and set up his own non-for-profit group, the Tony Blair Institute for Global Change, after leaving politics.

Each year, Royal Knights and Ladies of the Order of the Garter gather at St George’s Chapel in Windsor for a colourful procession and ceremony.

Crowds watch as they walk down the hill to the chapel from the state apartments, dressed in blue velvet mantles, red velvet hoods, black velvet hats and white ostrich plumes.

Sir Tony, who left Downing Street more than 14 years ago, is one of three new appointments announced by the palace.

Appointments to the Garter are in the Queen’s gift and made without prime ministerial advice, and are usually announced on St George’s Day, April 23, but she can do so at any time, and has chosen this one to coincide with the New Year Honours.