Tony Blair has won Commons backing to send UK forces into battle with Saddam Hussein - but also suffered another major backbench rebellion.
Blair: This is not the time to falter
Amid dramatic scenes in the Commons on Tuesday night, 217 MPs - 139 of them Labour backbenchers - backed a rebel amendment opposing the government's stance on Iraq, with 396 opposing the motion.
A motion backing the government's position was passed by 412 votes to 149.
There was relief for the government after fears that many more of Labour's backbenchers would oppose Tony Blair's line on Iraq.
But the revolt among Labour MPs was still up on the last vote with 139 backbenchers opposing Mr Blair compared to 122 at the last vote.
Fifteen Tories defied their leadership by voting against the government.
Support for the government motion fell by 22 votes to 412 from 434 when Iraq was last debated.
Rebel Graham Allen said the revolt was the largest ever against a Labour government.
"It's not something we wanted to have to do but it's a very strong message to the prime minister and I hope we can now all reflect carefully tomorrow on how we arrived at this situation again," he said.
But the government immediately rolled out big-hitting ministers to hail victory.
Within minutes of the vote being announced, Labour chairman John Reid told BBC News Online: "It is now clear that parliament has voted clearly to support the government in its efforts to disarm Saddam Hussein.
"Now that the democratic decision has been taken it is time for the country and parliament to unite."
And Mr Blair's official spokesman echoed the message, saying: "It is now time for all of us in Parliament and in the country to come
together and show the support our Armed Forces deserve."
The amendment drawn up by rebel MPs said there was no moral justification for war without a new UN resolution.
The vote followed more than nine hours of impassioned debate in the Commons during which the prime minister said Saddam Hussein would be strengthened "beyond measure" if the world fails to make Iraq disarm.
In one of the most important speeches of his career, the prime minister urged MPs "to give a lead, to show we will stand up for what we know to be right".
Mr Blair said the only people who would suffer if Saddam is not tackled would be the Iraqi people.
"Who will celebrate and who will weep if we pull our troops back now?" he said.
As Foreign Secretary Jack Straw wound up the debate there were protests from the public gallery in the Commons.
Outside, 200 - 400 protesters brought traffic to a standstill in Parliament Square.
One, 27-year-old Dan Kent, said: "I'm here because I don't believe in this war. It is essentially
US President George W Bush has given Saddam Hussein 48 hours to leave Iraq from 0100GMT on Tuesday.
The Iraqi leader has flatly rejected the ultimatum, while the White House has said US forces would enter Iraq to search for weapons of mass destruction even if Saddam does leave.
All UN inspectors have now left Iraq after President Bush's warning to Saddam.
The Commons debate took place as the prime minister suffered two more ministerial resignations from his government, but also saw another minister - Clare Short - saying she had decided to stay in her cabinet post as international development secretary.
She had earlier threatened to quit the government if the UK joined the US in action against Iraq without a second UN resolution.