If the West waits for a UN resolution until intervening in Syria, Britain would be "contracting out our foreign policy, our morality, to the potential of a Russian veto," David Cameron said in response to a question from ITV News deputy political editor Chris Ship.
"I think that is a very misguided approach," he said, describing last night's debate as "frustrating."
The G20 summit in St Petersburg exposed stark divisions between host Vladimir Putin and US President Obama over Syria.
War emptied the suburb of Yarmouk in southern Damascus of its people. Assad's army holds it, but their prize is a ghost town.
Even in the President's heartland of Baltimore, 95% of voters are against his policy on military intervention in Syria.