David Cameron is coming to the end of his remarks. He tells MPs "I know this is a highly complex situation" and that MPs will have further questions - which he hopes to answer from the despatch box today.

On the financing of IS, he says there are plans to intercept smugglers and sanctions against people who trade with IS. But he says the group is able to generate income through the control of its territory - which can only be countered by "rolling back" that control.

"This is an ISIL-first strategy", says David Cameron. "We are not naive to the complexity of the task," he adds, saying that the end goal is for inclusive governments in Iraq and Syria that command the confidence of all their peoples. He stresses once again that Syria's future cannot include President Assad.

David Cameron tells the House of Commons UK aid is helping to reduce the need for Syrians to flee to Europe. But he says MPs are right to ask questions on whether there'll be a proper post-conflict reconstruction effort, and says there will, adding that Britain will give at least an extra £1bn towards this task.

The prime minister says there are about 70,000 Syrian opposition fighters who don't belong to extremist groups who can help to defeat IS on the ground, among others.

He says that ultimately "a full political settlement" is needed - but argues that the UK should not wait for that before taking action.

David Cameron tells MPs the UK "is already in the top tier of countries that ISIL is targeting".

Turning to the legal basis for the UK extending its airstrikes against IS to Syria - he says there is a right of "self-defence".

The prime minister is now addressing the question, "why now?". He says that for as long as IS can "peddle the myth of its so-called caliphate" it will be "a rallying call for Islamist extremists all around the world" which, he says, "makes us less safe".

Moreover, the success in Iraq is put at risk by not being able to take action over the border in to Syria, he adds.

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Ahead of the PM's statement, Labour backbencher, Dan Jarvis, told the BBC "it is fair to say there are a range of views" within the shadow cabinet on Syria but that he hopes a consensus "can be reached". 

Mr Jarvis said the shadow cabinet would meet today after the Prime Minister's statement to the House. Mr Jarvis adds that "in the end, as individual members, we gave a responsibility to make a judgement". 

He went on to say that he will do what I thinks is the right thing based on his judgement as an individual Member of Parliament.

Why us, the PM asks? David Cameron tells MPs "we shouldn't be content with outsourcing our security to our allies", saying that if taking action in Syria can protect the UK "we should be helping allies", not "standing aside".

The reason for acting is because of "the very direct threat" that IS poses to the UK, David Cameron says, as he notes a series of terror attacks in Europe and beyond. He also tells MPs the UK has stopped seven terror attacks in the UK this year which were "either linked to IS or inspired by their propaganda".

The prime minister is on his feet, setting out the case for UK air strikes against the so-called Islamic State group in Syria. He says he wants to answer the following questions: why, why us, why now, is it legal, where are the ground troops to help meet the objective, what is the strategy, is there an end to this conflict, and a plan for what follows?

The Prime Minister has published his response, external to a recent Foreign Affairs committee report on air strikes in Syria ahead of a speech today.

It says: "The threats to our interests and to our people are such that we cannot afford to stand aside and not to act."

Mr Cameron warns of the threat posed by the militant group to the UK and says the country should not "sub-contract its security" to others.

Today Programme
BBC Radio 4

Chancellor George Osborne said earlier on his Today interview that the UK was already a "target" from so-called Islamic State, adding "we absolutely know they would like to carry out attacks in the UK if they could get away with it".

He says the UK isn't a country that relies on others to protect them and should be contributing. He adds the UK can bring "unique capabilities" but stresses a "political settlement" is needed in Syria along with work in the UK to ensure young people are not radacalised.

He says it is "strange" and "artificial" that pilots carrying out strikes in Iraq can not cross over to Syria and "take the fight to ISIL".

Victoria Derbyshire

Conservative MP Bob Stewart, a former army officer, says air strikes could stop so-called Islamic State in its tracks. But he says he is "amazed" there are so many aircraft over a small area without any coordination.

He says there are still questions around whose troops will be on the ground, adding if the threat of IS becomes too great then the UK should intervene.

Speaking about the death of civilians during air strikes Mr Stewart says the UK was "very accurate".

However Labour MP Madeleine Moon says she is concerned about Russian involvement saying "we're going to end up in a dog fight" with them.

Adding there are still problems in Iraq that the UK needs to help adding the Iraqis had asked for our help.