The UN Security Council tonight voted unanimously for a resolution calling on all member states that can do so to take military action against Isis in Iraq and Syria. After the decision it is likely a question of when, rather than if, the Commons will back UK air strikes in the latter. In response to the vote, David Cameron said:

"This is an important moment. Today, the world has united against ISIL. The international community has come together and has resolved to defeat this evil, which threatens people of every country and every religion.

"The United Nations Security Council has unanimously backed action against this evil death cult in both Syria and Iraq. It has also reiterated its determination to secure a political solution to the conflict in Syria.

"Today's vote shows beyond doubt the breadth of international support for doing more in Syria and for decisive action to eradicate ISIL. Britain will continue to support our allies who are fighting ISIL in Syria. I will continue to make the case for us to do more and to build support in Parliament for the action that I believe is necessary for Britain to take to protect our own security, as part of a determined international strategy. We cannot expect others to shoulder the burdens and the risks of protecting this country."

UN endorsement increases the chance that the majority of Conservative and Labour backbenchers will support air strikes. It also removes a central objection of the SNP to intervention. Jeremy Corbyn has long said UN backing is a pre-condition of military (unlike shadow foreign secretary Hilary Benn) but many believe that he will continue to oppose air strikes. He said on Thursday: "I'm not convinced that bombing would actually solve anything. We could end up with more civilian casualties and with an even worse situation in Syria."

But if Corbyn does oppose air strikes, it will now be far harder for him to deny Labour MPs a free vote (as he has so far done). As I noted earlier, the Labour leader supported the principle of free votes on military action in a 2013 speech. Denying a free vote on Syria would also make it harder for him to justify in the case of the divisive issue of Trident. Earlier tonight, in a letter leaked to The Staggers, former shadow minister Jamie Reed wrote to Corbyn demanding a free vote on Syria.

He wrote: "Clearly, any proposals brought forward by the government need to be considered, without prejudice and in forensic detail. It is not sensible to insist upon a whipped vote in the knowledge that such a move will likely mean that a significant number of colleagues will break the whip as a matter of conscience. Matters such as this – as your own voting record shows - will always be subject to individual conscience irrespective of the party whip. In short, a whipped vote with regard to any potential British involvement in Syria looks like a deliberate and calculated attempt to engineer a damaging and avoidable conflict within the PLP."

Update: Shadow foreign secretary Hilary Benn has welcomed the UN resolution but, as before, has emphasised that other tests remain. Here's his statement:

"I welcome the United Nations Security Council's unanimous approval of this resolution that urges UN member states to take all necessary measures to combat ISIL/Daesh in Iraq and Syria because of the unprecedented threat it represents to international peace and security.

“ISIL/ Daesh's depraved acts of violence have including subjecting women to unspeakable sexual violence, killing gay people and murdering innocent civilians in Paris, Egypt, Beirut, Ankara and Tunisia.

“I also welcome the progress that has been made in Vienna on a plan to end the Syrian civil war which will also help to defeat ISIL/Daesh by dealing with the chaos, violence and fear that allows it to thrive.

“The Security Council resolution must be seen as part of an overall effort to accelerate moves towards a comprehensive settlement of the conflict in Syria.

“As we have consistently said, Labour will judge any proposal the Government brings forward on British military action in Syria on the basis of what difference it would make to our objective of defeating ISIL/Daesh, its objectives, its legal basis and the views of other nations in the region. Crucially it must be part of a wider and more comprehensive strategy to end the threat they pose and achieve a negotiated solution to the Syrian civil war."

Update 2: The SNP has gone further than Benn in explicitly stating that it does not believe the UN resolution provides legal authorisation for military action. A spokesperson said:

"The resolution passed appears to be an enabling resolution and not a Chapter VII resolution requiring combined UN action to enforce peace in Syria. The Prime Minister should not therefore take it as authorisation for UK military action, which must be in line with international law.

"The SNP is prepared to listen to the Prime Minister’s case on military intervention - however, as well as its legality, he must address the efficacy of military intervention and how it will contribute to a wider initiative to end civil war and secure reconstruction. So far the case has not been made that the UK adding to the bombing of Syria will make any material difference in the campaign against Daesh.

"The UK is currently chairing the security council and should do much more to use its role to show urgency, to build on the peace plan which was started in Vienna last weekend, and to develop the plan for peace and reconstruction. Immediately this should involve a ceasefire among all non-Daesh forces in Syria as proposed by the U.S. Secretary of State this week."