DAVID Cameron has insisted there is a military, security and moral case for Britain launching air strikes against so-called Islamic State terrorists in Syria, telling MPs that inaction was now a greater risk than action.

In a House of Commons statement, the Prime Minister denied claims that extending airstrikes from Iraq to Syria would make the UK a bigger target for terror attacks, stressing how the country was already in the “top tier” of IS targets.

He highlighted the growing risk from IS, also known as Daesh, pointing to the recent attacks in Tunisia, Beirut, Ankara and Paris, and the downing of the Russian airliner over Egypt, as well as the seven terror plots foiled in the UK so far this year.

Mr Cameron explained how defence and security chiefs had advised him that not taking military action in Syria to degrade IS’s capability was a greater risk to Britain’s security than taking action.

He also noted how allies, like President Barack Obama of America and President Francois Hollande of France, wanted Britain to participate in the air strikes, and stressed to MPs that it was morally unacceptable to “outsource” to others the defence of the UK when the UK, through its military capabilities, could make a difference.

"We do face a fundamental threat to our security. We can't wait for a political transition, we have to hit these terrorists in their heartlands right now and we must not shirk our responsibility for security or hand it to others," declared the PM.

He went on: "Throughout our history the United Kingdom has stood up to defend our values and our way of life. We can, and we must, do so again."

Referring to the recent deadly attacks on Paris, Mr Cameron insisted: "If we won't act now, when our friend and ally France has been struck in this way, then our friends and allies can be forgiven for asking: If not now, when?"

In his response, Jeremy Corbyn, who in the past has been deeply opposed to any military intervention, raised a number of questions and warned of “mission creep” and “unintended consequences” of getting further involved with airstrikes on Syria.

The Labour leader asked the PM: "In the light of the record of western intervention in recent years, including Iraq, Afghanistan, and Libya, do you accept that UK bombing of Syria could risk more of what president Obama called unintended consequences? A lasting defeat of IS can only be secured by Syrians and their forces within the region."

Mr Corbyn made clear that IS, who opposed everything democracies like Britain stood for, posed a serious threat to the nation.

But he said the key question now was “whether extending the UK bombing from Iraq to Syria is likely to reduce or increase that threat and whether it will counter or spread the terror campaign IS is waging in the Middle East”.

Angus Robertson, the SNP's Westminster leader, made clear the Nationalists would not support a vote for military action unless key questions were "satisfactorily" answered. He and Alex Salmond, the party’s foreign affairs spokesman, received a briefing from intelligence chiefs on the IS threat.

He said: "Two years ago the Prime Minister urged us to bomb the opponents of Daesh in Syria. That would probably have strengthened this terrorist organisation. Today, he wants us to launch a bombing campaign without effective ground support in place or a fully-costed reconstruction and stability plan.

"The Prime Minister has asked us to consider his plan, we've listened closely. However, key questions posed by the Foreign Affairs Select Committee remain unanswered and unless the Prime Minister answers these questions satisfactorily the Scottish National Party will not vote for air strikes in Syria," he added.

Tory backbencher Crispin Blunt, who chairs the committee, offered his personal support to Mr Cameron's plan and said that in light of the peace talks in Vienna and the PM’s response it was now his personal view that “on balance, the country would be best served by this House supporting your judgement that the United Kingdom should play a full role in the coalition to best support and shape the politics, thus enabling the earliest military and eventual ideological defeat of IS”.

Earlier, Mr Cameron made clear he believed the recent UN resolution, which called for member states to take all necessary action to defeat IS, gave international legal authority to further airstrikes.

However, others disagree. Brenda O’Hara, the SNP’s defence spokesman, recently made clear that to have that legal authority Mr Cameron would have to get the specific sanction of a Chapter VII resolution at the UN.

The responses in the chamber showed that the PM still has work to do to get a Commons majority for further military action with differing views on different sides of the House.

Yvette Cooper, the former Shadow Home Secretary, said Mr Cameron had made a "strong moral and legal case" for tackling the "new totalitarianism" propagated by IS.

Tory MP Nadine Dorries noted: "If the attack, God forbid, had happened in London and not in Paris, I believe today the British people would be outraged, dismayed and upset that our allies did not have our backing and their politicians were taking so long to procrastinate about whether to come to their help."

Her Conservative colleague John Baron, just returned from the Middle East, said that the regional powers and allies felt that “in the absence of a realistic long-term strategy and proper local knowledge, we risk repeating the errors we made in Iraq, Afghanistan post-2006 and Libya”.

He insisted key questions remained unanswered and without them “air strikes will only reinforce the West's failure in the region generally at a time when already there are too many aircraft chasing too few targets".

Labour’s Paul Flynn, who represents Newport West, said the PM had been rightly commended for not lashing out militarily after the provocation of the atrocities of Tunisia in which Britons were murdered but added: “You are wrong now to ignore the real threat, the IS plan, which is to escalate a regional war into a world war between Christians and Muslims.”

In his contributions, Mr Cameron surprised MPs by referring to how analysis showed there were now 70,000-strong moderate force in Syria; this, he explained, was the "considered opinion" of the independent joint intelligence committee.

But, later, No 10 acknowledged that these forces were not under a unified control and operated in different parts of Syria yet they pointed out how they had successfully, in places, degraded IS’s military capability.

Following the Commons statement, the Shadow Cabinet met to discuss its way forward with the prospect of a vote in mind. While Mr Corbyn would like a unified approach, the divisions within Labour have been apparent and it might be difficult for Labour’s frontbench to agree one.

In any case, it is thought that as many as 70 Labour MPs might be prepared to vote with the UK Government for military action.

Given the Tory administration has a working majority of 16 and given Mr Cameron is keen not to suffer another humiliating defeat on a vote on Syria, his team are deeply anxious to ensure that their leader knows the numbers for and against as accurately as they can.

This means Labour’s approach is crucial and could be the difference between the PM calling a vote or not.

Earlier this week, he was keen to suggest time was of the essence and that every day MPs mulled over their options, IS was not being fully confronted. He said he would give them the weekend to consider their response to his statement.

This led to expectations that a vote would happen early next week. But the atmosphere in the chamber was not overwhelmingly positive for Mr Cameron. No 10, when asked about the timing of the vote, repeatedly said: “There is no timetable.”

The UK Parliament rises for Christmas in two weeks’ time and will not return until January 5.