Labour leader Sir Keir Starmer has dismissed criticism of Sir Tony Blair’s knighthood, insisting the former prime minister deserves the honour.

More than half a million people have signed a petition calling for Sir Tony’s appointment by the Queen to the Order of the Garter – the oldest and most senior British Order of Chivalry – to be rescinded over his domestic record and the Iraq War.

But Sir Keir, the MP for Holborn and St Pancras, insisted the honour is not a “thorny” issue and that Sir Tony had been a “very successful prime minister”.

The award could clear the way for Sir Tony’s successors in No 10 to be given similar honours, following reports that the delay in granting his accolade was blocking the others.

A Change.Org online petition calling for Sir Tony to be stripped of the honour had been signed by more than 565,000 people by Tuesday morning.

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.”

But Sir Keir told ITV’s Good Morning Britain: “I don’t think it’s thorny at all; I think he deserves the honour. Obviously I respect the fact that people have different views.

“I understand there are strong views on the Iraq War. There were back at the time and there still are, but that does not detract from the fact that Tony Blair was a very successful prime minister of this country and made a huge difference to the lives of millions of people in this country.”

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.