A petition to revoke the knighthood recently awarded to Tony Blair has reached 1m signatures in just six days.

Blair was made a Knight Companion of the Most Noble Order of the Garter, the oldest and most senior British order of chivalry, in the new year honours list.

But the honour for the former prime minister has provoked controversy.

On Friday afternoon, the Labour MP Richard Burgon tweeted: “It says a lot about what is wrong with our system when, after being one of the leading architects of the Iraq war, Tony Blair is honoured with a knighthood while Julian Assange, who exposed war crimes in Iraq, faces extradition to the USA and a lifetime in prison.”

However, the current Labour leader, Keir Starmer, has defended his predecessor’s record and said the honour was deserved, highlighting Blair’s achievements including bringing in the national minimum wage, setting up Sure Start centres for families and his efforts over the Northern Ireland peace process.

After the petition passed 500,000 signatures on Tuesday, Starmer said: “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.”

Angus Scott, who started the petition, wrote on Change.org: “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.”

On Thursday, as the petition approached 800,000 signatures, Scott thanked signatories on behalf of “families of soldiers who died in both Iraq and Afghanistan”.

He added: “For this petition to have any chance of having an effect, we must all unite to push it over 1m signatures. We can only do that if each and every one of you does your ‘bit’ to share the petition as widely as you can, to everyone you know and encourage them to do the same.”

Petitions on the parliament website are considered for debate by MPs if they pass 100,000 signatories, but petitions on Change.org, which describes itself as “the world’s platform for change”, have no more than a moral force.

Blair, who left Downing Street more than 14 years ago, was one of three new appointments to the Garter announced by the palace. Such moves are in the Queen’s gift, made without prime ministerial advice; and they are for life. Among those to have given their backing to the petition is Rose Gentle, whose 19-year-old son, Gordon, was killed by a roadside bomb in Basra in 2004. She told the Daily Record that she had written to the honours committee to ask for an explanation for Blair’s knighthood.

“Instead of standing in front of the Queen being made a Sir with that stupid grin on his face, he’d be better going to the cemetery and standing in front of my son’s grave to see what he’s done,” she said.