The British Prime Minister, Mr Tony Blair has suffered a backbench revolt in the Commons over his hardline stance on Iraq.
More than 100 Labour MPs are believed to have defied a three-line whip.
However the rebel amendment warning that the case for military action against Iraq was "as yet unproven" was defeated by 393 votes to 199.
The government had a majority of 194 thanks partly to Tory support.
But if the figure of 100 plus Labour rebels is confirmed by the division lists it will be the biggest rebellion since Mr Blair came to power in 1997.
The vote came after an impassioned full day's debate in which Labour former Cabinet ministers Mr Chris Smith and Mr Frank Dobson warned the time for war had not yet been reached.
Tory heavyweight Mr Kenneth Clarke weighed in behind them, warning that a war now could boost the terrorist threat and suggesting the course to war seemed to have been decided on months ago by the US.
Earlier, at question time, the Prime Minister had set out a staunch defence of his stance.