Shadow Chancellor John McDonnell likened a fellow Labour MP to Tony Blair after his speech backing Syria air strikes received mass applause in the House of Commons.
The shadow chancellor - who has said Mr Blair should be tried for war crimes - warned 'the greatest oratory can lead us to the greatest mistakes' in the aftermath of last night's vote by MPs .
Mr McDonnell has since expressed his sorrow on social media after MPs backed airstrikes by a 174-strong majority and 66 Labour MPs decided to back David Cameron 's stance in the free vote.
He told BBC Radio 4's Today programme: "I thought Hilary's oratory was great. It reminded me of Tony Blair's speech taking us into the Iraq War and I'm always anxious that the greatest oratories can lead us to the greatest mistakes as well."
The shadow chancellor was forced to deny he was calling his colleague a warmonger, adding: "I'm just saying sometimes the greatest oratory can lead us to the greatest mistakes and that's what we did in Iraq."
Mr McDonnell had previously backed a campaign seeing to arrest Tony Blair and bring him before the Hague.
In an interview in 2013, he said: "If we went to war on the basis of a lie, we need to bring the liars into court so we can then prosecute them for them."
Mr McDonnell now fears for innocent lives and the safety of our pilots and reiterated his belief that bombing is not the right answer on the radio programme.
He said "We're now engaged in war and... I'm hoping now we can come to a resolution so we can move beyond the military and arrive at a political solution."
"I thought the debate yesterday was excellent. We heard all the arguments. Hilary's speech was excellent and I thought the whole nature of the debate was very serious."