David Cameron and William Hague are seeking to outdo their French counterparts Francois Hollande and Laurent Fabius in warmongering rhetoric.
They admit to not having conclusive evidence that Syrian government forces used chemical weapons against opponents in Damascus.
But their demands for a military response presuppose that such evidence exists.
There are sound reasons for not believing that the Assad regime was responsible for a war crime that killed dozens and possibly hundreds of civilians in the Ghouta suburb of the Syrian capital.
Ever since Barack Obama warned that using chemical weapons would be a red line and that crossing it would entail serious consequences, Syrian government political and military commanders have known of the dangers that perpetrating such an atrocity would entail.
To do so while UN chemical weapons inspectors are actually in Damascus would be doubly reckless.
While Syria is still torn apart by a war between a ruthless government and an opposition reinforced by tens of thousands of non-Syrian jihadi fighters, the regime is less likely to be overthrown now than at any time in the two-and-a-half-year conflict.
There is no military reason for the Syrian National Army to resort such a desperate tactic.
It makes more sense in the warped logic of the al-Nusra Front - the al-Qaida allies providing the cutting edge of opposition military efforts and the authors of the allegation against government forces - to stage an act of barbarism to spur outside intervention.
Pro-interventionists insist that Nato should reprise its Libya option as though that represented an unalloyed success.
The western powers succeeded in getting rid of Muammar Gadaffi, although he posed no threat to their interests and had in fact co-operated with them.
However, Nato air power in support of the ragbag of anti-Gadaffi forces transformed Libya into a country without a functioning national government, dominated by local warlords competing for control of its hydrocarbon wealth and leaking well-armed jihadists into neighbouring states.
Nato military intervention in Syria would be even more catastrophic.
The al-Nusra Front has already threatened to attack villages in which Alawites live, confirming its essential religious sectarianism.
Tipping the military balance towards such elements by aerial bombing or cruise missiles launched by naval vessels in the Mediterranean against Assad forces would be folly of the highest order.
It could precipitate wider regional hostilities, opening up religious and political fault lines.
The US president, to his credit, has been openly sceptical of the benefit of any military intervention, raising international law and the need to be wary of "being drawn into very expensive, difficult, costly interventions that actually breed more resentment in the region."
However, with Britain, France and Israel champing at the bit, he will come under pressure from Capitol Hill to press the button.
The Assad government's agreement with the UN to deploy experts to the scene of the attack in Ghouta is very much to be welcomed.
The facts must be established as to the provenance of the chemical weapons and, if possible, who used them.
But the furore over this atrocity must not detract from the vital need to press ahead with negotiations between the government and its domestic opponents to end military conflict and develop Syrian democracy.