The UK Parliament vote to reject military action against Syria is a spectacular defeat for US foreign policy.

London has long been Washington's most loyal and unquestioning ally, always first in line to sign up for US-led wars. Under Tony Blair's leadership, Britain was arguably even more aggressive than the US, and was ridiculed as America's attack poodle.

There must now be increasing doubt that the US can rely on promised support from France. After meeting with Syrian opposition leader Ahmad al-Jarba, President Francois Hollande appeared to back away from earlier gung-ho statements, no doubt mindful that 59 percent of the French public are opposed to military action.

The UK vote has dealt a severe blow to the so-called R2P (Responsibility to Protect) doctrine that served as a justification for US-led attacks on sovereign states over the past decade and a half, starting with the 1999 bombing of Serbia.

Whatever the real motives for the invasions of Afghanistan and Iraq and the bombing of Serbia and Libya, a frequently stated reason was to protect the citizens of these countries from their own governments.

But far from protecting the innocent, the attacks killed them in their hundreds of thousands. As a result, the public no longer buys the argument. And it is no accident that the vote came at a time when trust in governments is at an all-time low as a result of Edward Snowden's revelations of mass snooping.

With hindsight, it is surprising the UK media did not see the government defeat coming. The proposed missile strikes against Syria had no public support, and there was no conclusive proof the Syrian government carried out the chemical weapons attack near Damascus. Perhaps most importantly, the strikes had no clear aim, save to "punish" the Assad government, after which the civil war would presumably continue as before.

It seems the UK government had an inkling of how the voting would go, which may explain its obscene abuse of opposition leader Ed Miliband.

The vote was always going to be a hard sell for Prime Minister Cameron and in the end it proved to be impossible.

Members of Parliament were being asked to back intervention in a civil war being fought largely on religious sectarian grounds, and make common cause not only with Gulf dictatorships like Saudi Arabia and Qatar but also with insurgents affiliated to al-Qaeda - heretofore known as the arch-enemy of Western civilization.

Britain would be supporting Sunni rebels against a government principally backed by the Alawites - a sect of Shia Islam - while in neighbouring Iraq a Shia government installed by the US is under attack by Sunni insurgents. Meanwhile the Syrian insurgents have driven tens of thousands of Syrian Kurds across the border into the Western-backed Kurdish enclave in northern Iraq. No wonder the Western public thinks its governments have lost the plot.

The UK Joint Intelligence Committee (JIC) – the same body responsible for the "dodgy dossier" used to justify the Iraq war – failed to produce conclusive evidence that the Syrian government had carried out the gas attack. JIC chairman Jon Day admitted being unable to explain "the regime's precise motivation for carrying out an attack of this scale at this time". This was probably the weakest point of the government's case. Given that Barack Obama had clearly stated that use of chemical weapons was a red line, why would Assad invite attack by brazenly crossing it?

Mr Day also mentioned "highly sensitive intelligence" but failed to reveal its content or source. He was probably referring to Israeli radio and telephone intercepts but did not say so because it would undermine the government's case to rely on information supplied by Israel, which has occupied Syrian territory since 1967, is the sworn enemy of one Syrian ally - Hezbollah, and is has been publicly urging an attack on another - Iran.

In terms of UK politics, the vote is a blow to the authority of Prime Minister Cameron and a severe personal setback for his foreign minister, the eternal Boy Scout William Hague. It will probably help Labour leader Ed Miliband who, after briefly wavering, came down on the side of public opinion and redrew the line - which had become blurred - separating him from the unpopular Blairites.

It remains to be seen if the US will now go it alone. President Obama and Secretary of State Kerry have invested a lot of political capital in this enterprise. But they also know that 60 percent of the US public are opposed to their plans.

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