The Government's Commons majority has been slashed to just 28 as it fought off a Tory motion calling for an immediate inquiry into the Iraq war.
The Government survived the Commons vote by 299 to 271 as 12 Labour rebels joined the Opposition parties to back an inquiry.
The result saw Labour's usual Commons majority of 67 cut by more than half, and represented an even tighter margin than a similar vote last June which the Government won with a majority of 35.
Opening the debate, shadow foreign secretary William Hague said that public opinion had now shifted behind the demands for an inquiry.
"If ministers continue to argue against that, they will be increasingly isolated voices holding out against a preponderance of national opinion," he said.
"They should not shirk this task because it seems unpleasant and should remember that if this inquiry is not established by this administration, it most surely will be by the next one."
Labour rebel Robert Marshall-Andrews (Lab, Medway) said the need for an inquiry was now "urgent, necessary and immediate".
"This isn't a war which is anywhere near its termination or end and that is why we cannot possibly wait until such time as that occurs," he said.
However, Foreign Secretary David Miliband said that, while the Government accepted the case for an inquiry, it should wait until British troops had completed their mission in Iraq.
"We think the priority of Government and our armed services should be to the situation in Iraq, not to the servicing of an inquiry," he said.
