SNP: there's no international legal authority to launch military airstrikes against Is in Syria

He has told MPs he will give them the weekend to consider his proposal with a vote expected early next week, possibly Monday.

SNP figures have already made clear more bombing will in itself not bring IS to book and what is needed is a unified diplomatic solution.

But Brendan O’Hara, the Nationalists’ defence spokesman, made clear that the United Nations resolution last week, which urged member states to “take all necessary measures” to combat IS, was not enough to give legal legitimacy to any further airstrikes.

The MP for Argyll and Bute made clear there had to be a so-called Chapter VII resolution first before the SNP would consider the PM’s proposal.

“The Government cannot come back and offer up what they have offered up in the past and expect us just to meekly accept what they offer up,” declared Mr O’Hara.

“There has to be a Chapter VII resolution and then, thereafter, we will look at what the Government has to say.”

The UN resolution said the Security Council was “determined to combat by all means this unprecedented threat to international peace and security” and called upon all member states to “take all the necessary measures” to combat IS.

A Chapter VII resolution explicity allows the Council to "determine the existence of any threat to the peace, breach of the peace, or act of aggression" and to take military and non-military action to "restore international peace and security".

While last week’s resolution was unanimously agreed, it is not certain a Chapter VII resolution would be. Moreover, it could take weeks for one to be put before the Security Council.

When it was put to him during a BBC interview that he was not satisfied with the UN resolution as a legal basis for further military strikes, Mr O’Hara replied: “I don’t think you can accept that the enabling resolution on Friday was a green light or has given legal legitimacy for military action. It has to be a Chapter VII resolution.”

Last week in the wake of the Paris terror attack, Nicola Sturgeon made clear she was “prepared to listen” to the case for extending air strikes in Syria, saying it would be "irresponsible" to do otherwise. But the First Minister also stressed that thus far the case had not been made.

Last month at its party conference, the SNP opposed UK military action in Syria; Alex Salmond, the former party leader, told delegates there should be "no more futile military interventions by the UK".

Meantime, Labour sources made clear that the Shadow Cabinet would meet on Thursday after the PM’s Commons statement and, again on Monday, to determine its response to the PM’s proposal.

One senior insider said that Jeremy Corbyn wanted to come to a collective decision but such are the  divisions within Labour on the issue that this might be impossible. It is thought that as many as 70 Labour MPs could vote with the Government to back airstrikes.

This would be more than enough for Mr Cameron to win a comfortable Commons majority even if there were some Tory rebels against extending military action to Syria.

If the vote for more airstrikes were won next week, then fresh military action could begin within days if not hours of the vote taking place.

In the Commons chamber, Philip Hammond, described IS as a "multi-tentacled monster" that could only be destroyed by targeting its headquarters in Raqqa.

The Foreign Secretary told MPs it was "morally unacceptable" to "outsource" the destruction of the terror group to other countries as he pressed the case for British military action in Syria.

During Commons question-time, he stressed some terror attacks carried out in the name of IS were "clearly" directed from Raqqa while others were inspired by the militants' "extremely effective" propaganda organisation, which was also run from the Syrian city.