The United States said it is still seeking to build an international coalition for possible punitive strikes on Syria following poisonous gas attacks last week it blames on the regime of President Bashar al-Assad.
A Syrian opposition official based in Turkey warned the British vote could encourage Assad to "use chemical weapons again on a much greater scale".
"It's regrettable that the British lawmakers were not able to understand the true situation in Syria," the official told AFP on condition of anonymity.
"The United States clearly said that Bashar crossed a red line and France has reiterated, through President (Francois) Hollande, its intention to participate," the official said.
"Even without the involvement of Britain, a lesson will be given to Bashar al-Assad.