Top Cabinet ministers would have resigned along with the prime minister if MPs had failed to back government policy during a key vote on Iraq.

It emerged on Saturday that Jack Straw was prepared to quit as foreign secretary if a majority of Labour MPs failed to back military action to disarm Saddam Hussein's regime.

And home secretary David Blunkett indicated that other ministers were prepared to follow Tony Blair out of government.

Straw was quoted in the Times as saying he considered resignation during the "very dark moments" in the run-up to the war.

And he told the Guardian that a lack of support in the Commons would mean that the prime minister "would almost certainly go and I would go with him".

The prime minister has already confirmed that he was putting his premiership on the line over the Iraq crisis.

He had told officials closest to him that he would leave Number 10 if he failed to secure the support of a majority of his own backbenchers.

Blunkett told the Guardian that everyone believed the prime minister had put his job on the line.

"I thought it would be a hit on the government as a whole," he said.

Geoff Hoon had also warned his US counterpart, Donald Rumsfeld, that Britain might not be able to take part in the military campaign if MPs voted against the government.

"The US came to understand it was about us gambling just about everything in getting this right," the defence secretary told the Guardian.