The prospect of British involvement in military action in Syria ended dramatically last night when David Cameron suffered a surprise and humiliating Commons defeat on the issue.

Despite concessions by the Prime Minister to opponents of military action, a rebellion by Conservative MPs and strong opposition by Labour saw the Government defeated by 285 votes to 272.

The vote leaves Mr Cameron's foreign policy in disarray and will raise new questions over his leadership. He is unable to deliver British support to American-led strikes on Syria over the Assad regime's alleged chemical weapons attack on civilians near Damascus. The vote will dismay the Obama administration, which is now likely to press ahead without the UK, perhaps as early as this weekend. One US military official said after the vote: “We care about what the UK thinks. We value the [Parliamentary] process but we're going to make the decision we need to make.”

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The rejected government motion said the response to the weapons attack “may, if necessary, require military action”. Although Mr Cameron promised a second vote next week before any British involvement, he failed to win support last night for what Labour described as a vote in principle for military action.

The Prime Minister immediately abandoned his plan for British involvement in Syria. He told MPs: “I strongly believe in the need for a tough response to the use of chemical weapons. But I also believe in respecting the will of this House of Commons. It is clear to me that the British Parliament, reflecting the views of the British people, does not want to see British military action. I get that and the Government will act accordingly.”

Philip Hammond, the Defence Secretary, confirmed there would now be no participation by the UK. He was “disappointed” by the Commons decision and admitted it would “place some strain” on the US-UK relationship. He blamed the Government's defeat partly on the the Iraq War, saying it had “poisoned the well” of public opinion, which had influenced MPs' votes.

The crushing blow for Mr Cameron is a huge coup for Ed Miliband, who toughened Labour's stance against military action after initially appearing ready to support it. The Opposition's line emboldened rebel Tory MPs. Many voted against a Labour amendment, calling for “compelling evidence” the Assad regime was responsible for the attack before UK involvement, which was rejected by 332 votes to 220.

But many Tories then refused to the support the Government's motion. Labour estimated that 30 Tories voted against, while others abstained. Amid farcical scenes, Justine Greening, the International Development Secretary, demanded a recount on the grounds that some ministers had missed the vote. She was rebuffed by the Speaker John Bercow. Michael Gove, the Education Secretary and a hawk on Syria, shouted “disgrace” at Tory and Liberal Democrat rebels. There was speculation that Tory whips had advised the Prime Minister not to recall MPs from their summer break for yesterday's emergency debate in the hope of winning endorsement for military action.

Earlier Downing Street accused Mr Miliband of giving “succour” to the Assad regime by opposing immediate military action against it.

The Independent has learnt that Mr Miliband toughened Labour's stance after being warned by Rosie Winterton, the Opposition Chief Whip, he would face a huge rebellion among the party's MPs if he supported military action. Some Labour insiders claim there could have been “one or more” resignations from the shadow Cabinet.

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Last night Jim Fitzpatrick quit as a Labour transport spokesman after telling the Commons he was “opposed to military intervention in Syria, full stop”. He voted against both the Government's motion and Labour's amendment to it, saying: “My objection is not having an exit strategy, not having an end game.”

Yesterday Britain sent six Typhoon jets to Cyprus to protect its bases against a strike from Syria, while the US and Russia both bolstered their naval forces in the Mediterranean in preparation for possible military action.

The Prime Minister's aides accused Mr Miliband of “flipping and flopping” and “moving the goalposts” only a day after the Labour leader had suggested he might support the Government, only to then demand a second vote in the Commons before any British strike was launched. The aides said Mr Cameron believed the Labour leader was “playing politics” and warned that the divisions displayed in yesterday's debate would give “succour” to the Assad regime.

Labour hit back angrily, accusing Number 10 of risking the political consensus the PM said he wanted to achieve. A Labour spokesman said: “That is frankly insulting. Language like that demeans Downing Street... It should not lower itself to the level of personal abuse.” He added: “It seems to us that it is uncalled for. There will be families up and down this country who are listening to this debate thinking that if there is military action it could be my son involved, it could be my father involved.”

Mr Miliband's tougher line won strong backing at a meeting of the Parliamentary Labour Party yesterday, but his aides denied he had been bounced into a U-turn by his own MPs. “It was about doing the right thing, not the numbers,” one said.

However, one Labour source admitted: “There was a big internal wobble after what Ed said on Tuesday. That led to quite a dramatic change of tone and a more aggressive stance.” Douglas Alexander, the shadow Foreign Secretary, is said to have played a key role. The discussions also included Tim Livesey, Mr Miliband's chief of staff, and Lord (Stewart) Wood, the shadow Minister Without Portfolio.

Mr Miliband said Labour wanted to see “compelling evidence” of the attack and a stronger commitment to involve the UN. He insisted that he did not rule out supporting military action.

Opening yesterday's debate, Mr Cameron conceded the British public was “war-weary” about getting involved in conflicts in the Middle East but insisted he would not repeat the mistakes of the 2003 invasion of Iraq. He was not proposing an invasion or taking sides in Syria, insisting: “We must not let the spectre of previous mistakes paralyse us.”

Tory ministers lose the plot

Tory ministers seemed to be losing the plot last night after three were reported to have missed the Commons vote, and one kept referring to the wrong dictator.

International Development Secretary Justine Greening and Africa Minister Mark Simmonds were both said to have missed the bell which sounded to let MPs know it was time to vote.

Meanwhile, a spokesman for former justice secretary and Minister without Portfolio Ken Clarke said he was unable to attend because of “logistical family reasons”.

In a later appearance on BBC Newsnight, Defence Secretary Philip Hammond seemed to repeatedly forget the country in which he wanted to see military intervention.

He twice referred to the need to prevent “Saddam Hussein” from using chemical weapons, in a reference to the former Iraqi despot who was executed in 2006.

Will Gant