David Cameron set out the case for air strikes against Islamic State militants after recalling Parliament for an emergency debate about taking on the extremists' "network of death".

The Prime Minister said there was "no more serious an issue" than deciding whether to commit British forces to the international effort to tackle IS and acknowledged the military effort would last "not just months, but years".

MPs will vote on whether to back the Royal Air Force joining the US-led bombing campaign, but British air strikes will be limited to Iraq rather than IS strongholds in Syria.

Opening the debate in the Commons Mr Cameron said: "The question before the House today is how we keep the British people safe from the threat posed by Isil and, in particular, what role our armed forces should play in the international coalition to dismantle and ultimately destroy what President Obama has rightly called this network of death.

"There is no more serious an issue than asking our armed forces to put themselves in harm's way to protect our country."

"This is not a threat on the far side of the world," Mr Cameron told MPs.

"Left unchecked, we will face a terrorist caliphate on the shores of the Mediterranean, bordering a Nato member, with a declared and proven determination to attack our country and our people.

"This is not the stuff of fantasy - it is happening in front of us and we need to face up to it."

The Prime Minister said he would set out why there was a direct threat to the UK, that there was a "comprehensive plan for dealing with the threat", that military action was necessary, including UK involvement, that it was legal, had the support of local partners and "added up to a moral justification for putting the lives of British service men and women on the line".

Outlining the domestic threat, he pointed out that the jihadist group had "already murdered one British hostage and is threatening the lives of two more", plotted attacks which would have affected British tourists and were "a terrorist organisation unlike those we have dealt with before".

Mr Cameron said there was "a strong case for us to do more in Syria" but recognised that it would require more work to secure Parliamentary approval of extending British involvement to that country. Mr Cameron said the military action would come as part of a "clear comprehensive plan" which included "tough, uncompromising" measures at home to prevent attacks.

These included previously-announced new powers to seize passports, strip British nationality from dual nationals and ensure airlines comply with no-fly orders.

"In all of this, we are being clear about the cause of the terrorist threat we face," said the PM. "That means defeating the poisonous ideology of Islamist extremism by tackling all forms of extremism, not just the violent extremists."

This involved banning preachers of hate and organisations which incite terrorism. "Of course, some will say that any action you take will further radicalise young people,"

Mr Cameron went on.

"I have to say this is a counsel of despair. The threat of radicalisation is already here. Young people have left our country to go and fight with these extremists.

"We must take action at home, but we must also have a comprehensive strategy to defeat these extremists abroad."

Labour veteran Dennis Skinner intervened to ask the Prime Minister: "How long will this war last and when will mission creep start?"

Mr Cameron replied: "This is going to be a mission that will take not just months but years, but I believe we have to be prepared for that commitment."

Continuing his answer to Mr Skinner's question,

Mr Cameron said: "The reason for that is, I think, quite rightly America, Britain and others are not contemplating putting combat troops on the ground.

"There will be troops on the ground but they will be Iraqi troops, they will be Kurdish troops, and we should be supporting them in all the ways that I will describe."

The Prime Minister said he was clear that the the rise of IS terrorists was down to the "poisonous narrative" of Islamist extremism that takes hold in broken states around the world. He called on Muslims to "reclaim their religion" from extremists, something he said is happening in Britain. He said: "We should be very clear that the cause of this problem is the poisonous narrative of Islamist extremism. "Wherever there are broken states, conflicts, civil wars, we see this problem arise. "Whether it is Boko Haram in Nigeria, whether it is al Qaida in the Yemen, or whether it is Isil in Iraq or Syria. "We need Muslims to reclaim their religion from these extremists. "That is happening in our country and happening around the world." Mr Cameron said the UK had a "duty" to take part and could not "subcontract" protecting British streets from terrorism to others. "Britain has unique assets that no other coalition ally can contribute," he said. "The Brimstone precision missile which minimises the risk of civilian casualties and which even the United States doesn't have. We have our unique surveillance and intelligence capabilities. We have highly professional forces which are well used to working with their US counterparts. "These are some of the reasons why President Obama made clear to me that America wants Britain to join the air action in Iraq. "But I believe it is also our duty to take part. "This international operation is about protecting our people too and protecting the streets of Britain should not be a task that we are prepared to entirely subcontract to other air forces of other countries." The Prime Minister admitted that air strikes alone would not solve the problem but insisted they were an indispensable part of a wider strategy. He said he agreed with UN Secretary General Ban Ki Moon's assertion that missiles can kill terrorists but it takes good governance to stamp out terrorism. Mr Cameron also accused Syrian President Bashar Assad of acting as a "recruiting sergeant" for extremists by "butchering his own people". Responding to an intervention from senior Tory Sir Edward Leigh, he rejected the allegation that the previous Iraq war led directly to the rise of IS. The PM said: "I am not claiming that by air strikes alone we can roll back this problem. "What this problem requires is a comprehensive strategy, including a well-formed Iraqi government and well-formed Iraqi armed forces because they in the end will be the ones who have to defeat this on the ground. "But where I disagree with you is the cause of how this came about. I would say that the two most principal causes of this problem as I have said - there is the background of Islamist extremism. "But the two principal causes are the fact that in Syria Assad has been butchering his own people and acting as a recruiting sergeant to the extremists, and secondly that in Iraq we had a Maliki government that did not represent all the people of Iraq. "I thought in one of the most powerful interventions I have heard him make, Ban Ki Moon got it spot on when he said that, look, missiles can kill terrorists, but it is good governance that will kill terrorism. "We should have that thought front and back of mind as we debate this afternoon." Mr Cameron outlined his strategy to use humanitarian and diplomatic efforts to combat the extremists, as well as disrupting their finances and the flow of foreign fighters through the UN. He went on: "Vitally, this strategy also involves political efforts to support the creation of a new and genuinely inclusive government in Iraq and to bring about a transition of power in Syria that can lead to a new representative and accountable government in Damascus that it too can take the fight to Isil. "But, yes, as one part of this comprehensive strategy I do believe that our military have an indispensable role to play." Mr Cameron said it was made clear to the Iraqi government that outside help was "conditional on you defending and protecting all of your people, and that must include the Sunnis in Iraq as well". He said he remained hopeful of support from "particular countries that may be able to encourage the Sunni tribes" to be involved in the fight. Mr Cameron said Iran had a "role to play" in addressing the crises in both Syria and Iraq. "The jury is still out on whether they will play that role but we should certainly be encouraging them to do that," he said. Mr Cameron met Iran's president Hassan Rouhani for historic talks at the United Nations earlier this week. The Prime Minister was challenged by former Foreign Office minister Alistair Burt about the UK's reluctance to supply arms to the Free Syrian Army. Mr Cameron told him there were no plans to provide weapons to the opposition forces in Syria. He backed the US-led air strikes against IS targets in Syria, but no British action can be taken there without a further debate and vote at Westminster. "I do believe there is a strong case for us to do more in Syria but I did not want to bring a motion to the House today which there wasn't consensus for," he said "It's better if our country can proceed on the basis of consensus." He added that he did not believe there was a "legal barrier" to action in Syria but he acknowledged the situation there was "more complicated" than in Iraq because of the civil war and the position of President Assad. Mr Cameron said the air action that has already taken place in Iraq has made a difference, saving the lives of minorities who "otherwise would be butchered" by IS. Setting out why he believed military action was necessary, he said "without it I don't believe there is a realistic prospect of degrading and defeating Isil". He added: "There already is a military conflict taking place. Isil have taken territory, they are butchering people in Iraq. "Iraqi, including Kurdish, security forces are already fighting Isil. We have to decide if we are going to support them, and I believe that we should. "In Iraq, the real work of destroying Isil will be for the Iraqi security forces. But they need our military help." Mr Cameron said that even if IS are defeated, Britain will be dealing with the problem of Islamist extremism for many more years. He said: "Even after Isil has been dealt with, we should be in no doubt that future British prime ministers and future British governments, I suspect, will be standing at this Despatch Box, dealing with this issue of Islamist extremism in different forms and in different parts of the world for many years to come. "Isil has sprung up quickly but around the world we see the mayhem caused by other groups, whether that is Boko Haram in Nigeria, al-Shabaab in Somalia, al Qaida in Yemen. "We are dealing here with a generational struggle caused by the perversion of one of the world's great religions, Islam. "But I have no doubt that this struggle is one which this House and this country is more than equal to." The PM reiterated that his ability to take specific military action without the approval of MPs if responding to an imminent humanitarian catastrophe or if a crucial British interest was under threat. He said: "I think the convention that has grown up in recent years that the House of Commons is properly consulted and has a proper vote is a good convention and I think is particularly apt when there is, as there is today, a proposal for, as it were, premeditated military action. "But I think it's important to reserve the right that if there was a critical British national interest at stake or if there was the need to act to prevent humanitarian catastrophe then you could act immediately and explain to the House of Commons afterwards. "I'm being very frank about this because I don't want to mislead anybody." Mr Cameron said more had to be done to persuade former backers and funders of Isil - including key Western allies such as Saudi Arabia, Kuwait and Qatar - that they had made a "terrible mistake" that contributed to creating the present crisis. "There is more that needs to be done to persuade those that in the past might have backed organisations like Isil because they were seen as a Sunni Arab organisation that they made a terrible mistake and they should not do it again," he said. "That was very much what was being discussed around the table at the UN Security Council and an issue I support. "We need to have this very direct conversation with everyone in the Middle East which is the dangers of this sectarianism, supporting groups because they are Sunni or because they are Shia. "That is part of the background that has led us to this problem." The PM said the shadow of the 2003 decision to join the US-led invasion of Iraq "hangs heavy" over today's vote but told MPs: "We must not use past mistakes as an excuse for indifference or inaction. "We will play our part in destroying these evil extremists, we will support our Muslim friends around the world as the reclaim their religion and, once again, our inspirational armed forces will put themselves in harm's way to keep our people and our country safe. "I pay tribute to their extraordinary bravery and service." He insisted that he was "not contemplating the use of British combat forces" as that was not the "most appropriate role for us". And he played down the criticism of Tory MP James Gray that the Government found itself "hamstrung" in being able to take appropriate action because of the need to have Labour's support for any commitment. "Is there not a place here for leadership and statesmanship rather than popular support of the country. He needs the support of the country but do we really need a vote?" Mr Gray said. Mr Cameron said it was right in a "robust democracy" that Parliament should have the chance to vote on military action in such pre-meditated circumstances. mfl Page 11: 12:05 Labour leader Ed Miliband acknowledged that there was "unease" about intervention following the 2003 Iraq War but said "we cannot simply stand by" against the threat of IS. He said: "As we debate this issue today, I understand the qualms and, for some, deep unease that there will be about this undertaking both in this House and in the country. "Those who advocate military action today have to persuade members of this House not just that Isil is an evil organisation but that it is we, Britain, who should take military action in Iraq." Mr Miliband said IS was targeting "anyone who does not subscribe to its deeply perverted ideology". "Let's be clear about what this is: Isil is murdering Muslims," he said. "So, to those who say that military action against Isil is somehow an attack on Islam, let me just say this: I understand the anxiety, including communities in Britain. "But the truth is entirely different." The ideology of IS had "nothing to do with the peaceful religion practised by billions of people across the world and by millions of our fellow citizens, who are appalled by their actions", he said. "Isil is not simply a murderous organisation; it has ambitions for a state of its own - a caliphate across the Middle East, run according to their horrific norms and values. "That's why I believe ... we cannot simply stand by against the threat of Isil." He said action against IS met his six criteria for intervention: there was a just cause, it was a last resort, there was a clear legal base, military action had a reasonable prospect of success, it had regional support, and was proportionate. The Labour leader said the legacy of the Iraq War meant there was a "heightened responsibility" on the UK to support the country's government. Quoting Robin Cook's resignation speech on the eve of the Iraq War, Mr Miliband said the former foreign secretary and leader of the Commons had told MPs "our interests are best protected not by unilateral action but by multilateral agreement and a world order governed by rules". Mr Miliband said: "This is multilateral action prompted by a legitimate, democratic state. "And a world order governed by rules, if it is about anything, must be about protecting a democratic state." Mr Miliband's refusal to back military action against the Assad regime in Syria last year led to a humiliating Commons defeat for the Prime Minister. The Labour leader said he had reservations about any future move to target IS in Syria. "We will consider any further proposition, if the Prime Minister so chooses to come back with it," he said. But there was a question of legitimacy, he said, and although there was a "strong argument" that action in Syria may be legal, "it would be better to seek a UN Security Council resolution". In Iraq, a ground campaign was being fought by Iraqi and Kurdish forces but in Syria "there is an outstanding question about who will perform that function". There was also a "big outstanding question" about the "overall outcome" being sought for Syria. But Tory John Baron, who warned the Prime Minister that military action could be "counter-productive", said there was "no clear exit strategy" from intervention in Iraq.