Former Conservative Defence Secretary Dr Liam Fox says the question boils down to this: "Whether we confront them over there or increasingly take the risk of confronting them over here." David Cameron says his analysis is spot on, warning that "inaction is the greater risk".

Julian Lewis, who chairs the Defence Select Committee, says IS "must be crushed militarily in Syria". He notes that David Cameron has said air strikes alone will not be effective and must be in co-ordination with credible ground forces. But he says the PM's claim that there are 70,000 non-extremist fighters in the region "is a revelation to me", and says the Syrian army must be involved.

Former government chief whip Andrew Mitchell rises to support the prime minister, saying his case for bombing IS targets in Syria is "compelling". David Cameron is "very grateful" for his support, and tells MPs the action "will help to make us safer".

Labour MP David Winnick recalls the 2013 Commons vote on military action  against Syrian President Bashar al-Assad's government. He says it was the right decision by MPs to vote against, and argues that air strikes now won't make any difference "at all" in defeating IS. David Cameron disagrees.

Conservative MP Ken Clarke, a former cabinet minister, says the PM's case is "compelling".

He asks whether David Cameron accepts that in the medium-term the UK must look at "whatever agreement" is necessary to secure a political solution in Syria, cautioning that it may fall "far short of what a liberal Western democracy might look like".

David Cameron says that "yes of course, that is likely". But he maintains that President Assad cannot remain in power because he doesn't have the support of all his peoples.

Angus Robertson says the PM is asking for support for a bombing campaign in Syria "without effective ground support" or "a fully-costed reconstruction plan" for Syria. Key questions remain unanswered and unless they are addressed, the SNP "will not vote for airstrikes in Syria", he tells the House

SNP Westminster leader Angus Robertson says the party shares concerns "about the terrorist threat" from IS. He says the SNP strongly supports a ceasefire in Syria and a political solution to the Syrian conflict - and asks the PM what the UK is doing to support these efforts.

He also repeats a question he put to David Cameron at PMQ's yesterday, asking what forces will actually get involved on the ground to defeat IS.

Foreign Affairs Committee chairman Crispin Blunt, whose committee has warned against air strikes against IS in Syria, asks the PM if he says getting the politics right in Iraq and Syria is "the immediate and overriding priority".

He says the committee will discuss its collective view on the PM's case and asks the PM to give evidence in two months' time on the implementation of the strategy. He then offers his personal view, which is that: 

David Cameron says Syria cannot have a future if IS continues to control its territory and grow its so-called caliphate, as he responds to Jeremy Corbyn's comments.

He also says the "poisonous narrative" of Islamist extremism is "a battle for our generation", and must be combated - not just through military action, he says, but also argument, for example.

"We are not going to deploy British combat forces," David Cameron tells MPs. He says the presence of Western boots on the ground in Syria would be "counter-productive". One of Jeremy Corbyn's questions was to ask for a commitment not to send British ground forces in.

The final question from Jeremy Corbyn is "in the light of the record of Western military intervention in recent years" whether he accepts that UK bombing of Syria could risk more "unintended consequences" and that a lasting defeat of IS can only be achieved by Syrian forces in the region

Responding, David Cameron commends his opposite number's "quite correct caution" over military action, but says he believes there is "a good answer" to all of his questions.

Labour leader Jeremy Corbyn also asks David Cameron to rule out deployment of British ground forces to Syria. He's concerned about "mission creep" without any "credible and acceptable forces" in Syria to combat the jihadist group.

Labour leader Jeremy Corbyn responds to the PM's statement. He says the first priority has to be the security of the British public. There's "no doubt" IS has imposed a "reign of terror" on millions of people, he tells MPs.

The question is whether extending UK bombing from Iraq to Syria is likely to reduce or increase that threat, and combat terrorism, he says. He has seven questions for the PM, including whether he believes that air strikes in Syria will make "a significant military impact on the ground" and if he expects it will be a "war-winning strategy".

David Cameron: "We will not beat ISIL if we waiver in our view that Assad must go."

He reiterates that there won't be a Commons vote unless there's a clear majority for action so as to avoid a "publicity coup" for so-called Islamic State.