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appointment by the Queen to the Order of the Garter – the oldest and most senior British Order of Chivalry – to be rescinded over his domestic record and the Iraq War.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 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 the 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 544,000 people by Tuesday morning.

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.”

Meanwhile, vaccines minister Maggie Throup told LBC: “I think he did lots of good things. And I think it’s only right that we do honour our previous prime ministers. And he was prime minister for such a long time.”

In a hint that Gordon Brown, David Cameron and Theresa May could be in line for honours, she said: “I think obviously it now opens the doors for others to be recognised in the same way.”

Commons Speaker Sir Lindsay Hoyle has suggested that all former prime ministers should be offered a knighthood because “it is one of the toughest jobs in the world”.