New Labour leader Ed Miliband today conceded the conflict in Iraq had divided the country and said Tony Blair's government was "wrong" to go to war.
In a frank admission to the party's annual conference in Manchester, Mr Miliband said the Labour government had "undermined" the United Nations.
"Iraq was an issue that divided our party and our country. Many sincerely believed that the world faced a real threat.
"I criticise nobody faced with making the toughest of decisions and I honour our troops who fought and died there. But I do believe that we were wrong. Wrong to take Britain to war and we need to be honest about that.
"Wrong because that war was not a last resort, because we did not build sufficient alliances and because we undermined the United Nations.
"America has drawn a line under Iraq and so must we," said Mr Miliband, drawing applause from delegates.
He added that British troops were in Afghanistan to stabilise the country and enable a political settlement to be reached.
"I will work in a bipartisan way with the Government to both support our mission and ensure Afghanistan is not a war without end."
Mr Blair has been dogged by his decision to take the UK to war in Iraq but has never apologised or said he made a mistake.
Mr Miliband said "old thinking" on foreign policy should be challenged, adding: "We are the generation that came of age at the end of the Cold War.
"We are the generation that recognises that we belong to a global community - we can't insulate ourselves from the world's problems."
The Labour leader was warmly applauded when he said: "Our alliance with America is incredibly important to us but we must always remember that our values must shape the alliances that we form and any military action that we take."
Tony Woodley, joint leader of Unite, said Mr Miliband had addressed the "illegal" war in Iraq, adding: "At long last, we have an acknowledgement that the Iraq war was a stain on the character of our party."