A government motion was defeated by 285 to 272, a majority of 13 votes.

Prime Minster David Cameron said it was clear Parliament does not want action and “the government will act accordingly”.

It effectively rules out British involvement in any US-led strikes against the Assad regime.

Labour leader Ed Miliband said the vote meant military action was “off the agenda”, and added that MPs had reacted against the prime minister’s “cavalier and reckless” leadership.

The defeat comes as a potential blow to the authority of Mr Cameron, who had already watered down a government motion proposing military action, in response to Labour’s demands for more evidence of Assad’s guilt.

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White House deputy press secretary Josh Earnest said Thursday that the British foreign secretary has recognized America’s “right and ability” to make its own foreign policy decisions with regard to the crisis in Syria.

Earnest’s press conference came mere hours before British Parliament voted down the possibility of British military intervention in Syria, for which prime minister David Cameron was advocating. Cameron acknowledged Parliament’s decision and said “the government will act accordingly.”

But even though Britain won’t be joining in potential strikes on Syrian dictator Bashar al-Assad, the British government already granted the United States permission to make its own Syria decisions, according to Earnest.

“And we’ve also seen an acknowledgment from the [UK] foreign secretary about the United States’ right and ability to make our own foreign policy decisions that are in our national security interest,” said Earnest, who went on to read British Foreign Secretary William Hague’s statement granting decision-making independence to the commonwealth’s former American colonies.

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But the push for strikes against the Syrian regime began to lose momentum as questions were raised about the intelligence underpinning the move. During a debate with lawmakers, he conceded that there was still a sliver of uncertainty about whether Assad truly was behind the attacks.

“In the end there is no 100 percent certainty about who is responsible,” Cameron said, although he insisted that officials were still as “as certain as possible” that Assad’s forces were responsible.

That was not enough for Britain’s Labour Party, which is still smarting from its ill-fated decision to champion the invasion of Iraq in 2003. The party announced its opposition to the move despite Cameron’s concessions, which included a promise to give U.N. inspectors time to report back to the Security Council and to do his outmost to secure a resolution there.

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The opposition to President Obama launching unilateral military operations in Syria exploded on Thursday when dozens of liberal Democrats joined scores of conservative Republicans in warning the administration that any strikes without congressional approval would violate the Constitution.

In a letter to Obama, 53 liberal Democrats — including a long list of Congressional Black Caucus (CBC) members — argued that, while the human rights atrocities being committed by the forces of Syrian President Bashar Assad are “horrific,” they alone “should not draw us into an unwise war – especially without adhering to our own constitutional requirement.”

“While we understand that as Commander in Chief you have a constitutional obligation to protect our national interests from direct attack, Congress has the constitutional obligation and power to approve military force, even if the United States or its direct interests (such as its embassies) have not been attacked or threatened with an attack,” reads the letter, which was spearheaded by Rep. Barbara Lee (D-Calif.), a former head of the CBC.

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President Obama is prepared to move ahead with a limited military strike on Syria, administration officials said on Thursday, even with a rejection of such action by Britain’s Parliament, an increasingly restive Congress, and lacking an endorsement from the United Nations Security Council.

Although the officials cautioned that Mr. Obama had not made a final decision, all indications suggest that the strike could occur as soon as United Nations inspectors, who are investigating the Aug. 21 attack that killed hundreds of Syrians, leave the country. They are scheduled to depart Damascus, the capital, on Saturday.

The White House is to present its case for military action against Syria to Congressional leaders on Thursday night. Administration officials assert that the intelligence will show that forces loyal to President Bashar al-Assad carried out the chemical weapons attack in the suburbs of Damascus.

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The “special relationship” has just become less special. One reasons links between Washington and London have generally been so close is that they could generally rely upon us in a fight. Now they can’t. And that might be because …

Britain is becoming less imperialist, and more European. This is probably the most important lesson to be learnt from tonight’s vote. In the past prime ministers have justified interventionist policies on the grounds that Britain is an outward-looking power that gets involved in the world, that tends to gets “stuck in”. This is normally explained as a legacy of our imperial past. But the public seem to have had enough. Any more wars? No thanks. We’re turning German. And that affects what the government does because …

Parliament matters more. Technically prime ministers do not need the support of the Commons to go to war. Sending troops into action is a prerogative power (meaning it can happen just on the prime minister’s say so). But Tony Blair allowed a vote on the Iraq war, and since then parliament has been flexing its muscles even more. Of course having a hung parliament helps. But this might be a good night to remember Robin Cook, whose gravestone carries the words: “I may not have succeeded in halting the war, but I did secure the right of parliament to decide on war.”