More than 600,000 people have signed a petition calling for former Prime Minister Sir Tony Blair to have his knighthood removed.
The ex-Labour leader, who was in power from 1997 to 2007, was given the title as the New Year's Honours were awarded.
But the petition complains that his role in the Iraq war makes him "personally responsible" for many deaths and accuses him of "war crimes".
Labour leader Sir Keir Starmer said Sir Tony had "earned" a knighthood.
And a government minister said it was "only right" to reward the former prime minister, who had done "many good things" for the UK.
On 1 January, Sir Tony became a member of the Order of the Garter, England's oldest and most senior order of chivalry.
The appointment was the personal choice of the Queen, who has up to 24 "knight and lady companions", with current Prime Minister Boris Johnson not involved in the decision.
But a petition posted on the change.org website by Angus Scott says Sir Tony "caused irreparable damage to both the constitution of the United Kingdom and to the very fabric of the nation's society" while in office.
"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," it adds.
"Tony Blair is the least deserving person of any public honour, particularly anything awarded by Her Majesty the Queen."
The petition is unlikely to result in Sir Tony's knighthood being rescinded.
Unlike the New Year's Honours list, which is drawn up by the government for the Queen's approval, the Order of the Garter is bestowed as a personal gift by the Queen.
The Honours Forfeiture Committee cannot recommend the removal of knighthoods handed out in this way.
Sir Keir, a former director of public prosecutions who received his own knighthood for services to law and criminal justice in 2014, said: "I don't think [Boris Johnson] has earned the right to a have an honour. I do think Tony Blair has."
Conservative minister Maggie Throup told LBC radio: "[Tony Blair] did lots of good things and it's only right that we do honour our previous prime ministers."
Of the other four living former prime ministers, only Sir John Major has received a knighthood-level honour, with Gordon Brown, David Cameron and Theresa May as yet missing out.
But Ms Throup, the vaccines minister, said Sir Tony's award "now opens the doors for others to be recognised in the same way".
Labour MP Peter Kyle, a supporter of Sir Tony, told BBC Radio 4's World at One: "I'm happy about the knighthood. I'm talking to you as a gay man. Almost all the freedoms I enjoy as such were granted by the Blair government.
"Do I think he deserve a knighthood? I think he deserves a knighthood for that alone".
In 2009, US President George W Bush presented Sir Tony with the Presidential Medal of Freedom - the highest US civilian honour - for "efforts to promote democracy, human rights and peace abroad".
But the 2016 Chilcot report into the UK's involvement in the Iraq war found Sir Tony's government had chosen to join the US-led invasion before all peaceful options for disarmament had been exhausted.
It also said planning and preparations for the country after the deposing of Saddam Hussein had been "wholly inadequate".
The ex-Labour leader, who was in power from 1997 to 2007, was given the title as the New Year's Honours were awarded.
But the petition complains that his role in the Iraq war makes him "personally responsible" for many deaths and accuses him of "war crimes".
Labour leader Sir Keir Starmer said Sir Tony had "earned" a knighthood.
And a government minister said it was "only right" to reward the former prime minister, who had done "many good things" for the UK.
On 1 January, Sir Tony became a member of the Order of the Garter, England's oldest and most senior order of chivalry.
The appointment was the personal choice of the Queen, who has up to 24 "knight and lady companions", with current Prime Minister Boris Johnson not involved in the decision.
But a petition posted on the change.org website by Angus Scott says Sir Tony "caused irreparable damage to both the constitution of the United Kingdom and to the very fabric of the nation's society" while in office.
"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," it adds.
"Tony Blair is the least deserving person of any public honour, particularly anything awarded by Her Majesty the Queen."
The petition is unlikely to result in Sir Tony's knighthood being rescinded.
Unlike the New Year's Honours list, which is drawn up by the government for the Queen's approval, the Order of the Garter is bestowed as a personal gift by the Queen.
The Honours Forfeiture Committee cannot recommend the removal of knighthoods handed out in this way.
Sir Keir, a former director of public prosecutions who received his own knighthood for services to law and criminal justice in 2014, said: "I don't think [Boris Johnson] has earned the right to a have an honour. I do think Tony Blair has."
Conservative minister Maggie Throup told LBC radio: "[Tony Blair] did lots of good things and it's only right that we do honour our previous prime ministers."
Of the other four living former prime ministers, only Sir John Major has received a knighthood-level honour, with Gordon Brown, David Cameron and Theresa May as yet missing out.
But Ms Throup, the vaccines minister, said Sir Tony's award "now opens the doors for others to be recognised in the same way".
Labour MP Peter Kyle, a supporter of Sir Tony, told BBC Radio 4's World at One: "I'm happy about the knighthood. I'm talking to you as a gay man. Almost all the freedoms I enjoy as such were granted by the Blair government.
"Do I think he deserve a knighthood? I think he deserves a knighthood for that alone".
In 2009, US President George W Bush presented Sir Tony with the Presidential Medal of Freedom - the highest US civilian honour - for "efforts to promote democracy, human rights and peace abroad".
But the 2016 Chilcot report into the UK's involvement in the Iraq war found Sir Tony's government had chosen to join the US-led invasion before all peaceful options for disarmament had been exhausted.
It also said planning and preparations for the country after the deposing of Saddam Hussein had been "wholly inadequate".
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