David Cameron told MPs that attacking Islamic State in Syria would help make the United Kingdom safer, adding that the country could not outsource its security to others.
In a lengthy statement outlining the case for extending airstrikes into Syria, and during a two-hour debate that followed, Mr Cameron said this month's attacks in Paris could just as well have been in London.
"If we believe that action can help protect us, then, with our allies, we should be part of that action, not standing aside from it," he said. "From that moral point comes a fundamental question: if we will not act now, when our friend and ally, France, has been struck in this way, then our allies in the world can be forgiven for asking, 'If not now, when?' "
The prime minister hopes to put military action to a vote next week but would do so only if he was confident it had the backing of a “clear majority”.
He said a long-term solution in Syria could be achieved only through a combination of counterterrorism, political and diplomatic engagement, and military and humanitarian action.
Political transition
“We know that peace is a process, not an event. I am clear that it cannot be achieved through a military assault on ISIL [Islamic State of
Iraq
and the Levant] alone; it also requires the removal of Assad through a political transition.
“But I am also clear about the sequencing that needs to take place. This is an ISIL-first strategy,” he said.
Labour leader Jeremy Corbyn sought more detail on the likely efficacy of UK airs strikes in Syria and asked for an assurance that British ground troops would not be deployed there. Mr Cameron ruled out sending ground troops but the Labour leader made plain his scepticism about the usefulness of western military action in the region.
"In the light of the record of western military interventions in recent years, including in Iraq, Afghanistan and Libya does the prime minister accept that UK bombing of Syria could risk more of what President Obama called 'unintended consequences' – and that a lasting defeat of Isis can only be secured by Syrians and forces from within the region?" he said.
Shadow cabinet
Labour’s shadow cabinet met after the debate but postponed until Monday a decision on how MPs should vote, and if they should be whipped or allowed a free vote.
Mr Corbyn and some of his close allies in the shadow cabinet oppose military action but most Labour frontbenchers are understood to favour it.
The Scottish National Party's Angus Robertson said that, like the Labour leadership, he had received a national security briefing on the threat from Islamic State, also known as Isis, on Wednesday night. But he suggested his party would still vote against military action on the basis there were too many "unanswered questions".
The Democratic Unionist Party's Nigel Dodds said he could see the case for attacking Islamic State but warned past foreign policy failures had sapped popular enthusiasm for military intervention in the Middle East.
