As the statement exceeds the two and a half hour mark, it looks like there's just a handful of MPs left to question the PM. This is on track to be one of the longest statements seen.

Labour's Ynys Mon MP, Albert Owen, asks the PM: "If increased bombing leads to increased refugees" will he revise his pledge to take 20,000 Syrian refugees in the UK by 2020?

David Cameron says the government keeps its plans under review, but adds that the crucial thing is to get on with it, adding that he's "confident" 1,000 refugees will arrive here by Christmas.

Ronnie Cowan, of the SNP, takes objection to the PM urging MPs to separate this case from the Iraq War, after several of them raised it in their questions. Mr Cowan says that "if we don't look back, we don't learn anything".

He tells the PM that had the Chilcot Inquiry into the 2003 war been published by now (it began its work in 2009 and has been heavily criticised for the delays) "we'd be better informed as to how best to handle this complex situation".

David Cameron says that "had we had our way the report would have been published by now". He also clarifies that he's not telling MPs not to learn the lessons from Iraq, but making the point that "we shouldn't enter a freeze where we're incapable of making decisions that are necessary" to keep the UK safe.

SNP MP Patrick Grady asks how the £1bn the UK has promised to spend on reconstructing Syria will compare with the total cost of planned military action, saying the Libya intervention cost "13 times as much".

David Cameron tells him it'll depend on how long the campaign lasts and how great the need is in Syria. But he adds that the UK aid budget "is almost unrivalled" anywhere in the world.

Andrew Percy, the Conservative MP for Brigg and Goole, voted against military action in Syria, in 2013. But he says it's "increasingly likely" that he will support the proposed airstrikes "as long as it is against ISIS and not ground troops".

If the prime minister gets his way and Parliament does give the go-ahead for Britain to join in air strikes against IS in Syria then there are a number of facts people should know. 

This will not lead to the immediate or even imminent demise of so-called Islamic State. 

It will simply add to the incremental damage being done over time to this proscribed terrorist group by other air forces already bombing in Syria. 

IS's centre of gravity is around Raqqa, in Syria. Britain is already at war with IS next door in Iraq, where the RAF has been hitting their positions for more than a year. 

So Britain is already a target for IS-inspired terrorist attacks, including some of the seven thwarted in the UK in the last year. 

But IS will be acutely aware of this very public debate and will very likely look to "punish" Britain in the way it has already targeted France. 

So in the short to medium term this would increase - but not initiate - the terrorist threat to UK.

Labour MP and former soldier Dan Jarvis says "necessary" military action must go alongside a political settlement in Syria. David Cameron agrees, and says he wouldn't back air strikes if he thought it would derail a political process.

SNP MP Lisa Cameron invites the prime minister to say for how many months UK air strikes could, and will, be sustained.

David Cameron says he doesn't want to put a time-frame on it as it will depend on the success of the mission. But he says the UK's allies see it as a "valuable" contributor because the "strength and stability" of our air force means it can sustain air strikes "at a regular tempo of combat" rather than"surge them up and surge them down".

Clive Efford, Labour's Eltham MP, says he accepts the threat IS poses to the UK regardless of whether Britain extends military action to Syria. But he wants more information from the government about who will occupy and control the territory in Syria if IS is forced into retreat.

David Cameron tells him there "isn't a perfect situation in Syria of huge amounts of grounds forces", but adds that it "would be wrong to suggest there aren't any".

Noting the number of MPs hoping to question the PM, Speaker John Bercow appeals for short questions from MPs "without preamble", to speed the session along.

Kate Hoey, Labour MP for Vauxhall, seeks confirmation that the government is not seeking regime change in Syria with its proposed bombing campaign. David Cameron gives her that assurance, saying it's about "degrading and destroying" IS. But he says the government does believe that ultimately a political transition is needed in Syria.

The Conservative MP for Gillingham and Rainham, Rehman Chishti, continues his campaign for the government to refer to the terrorist group as Daesh, rathern than IS, so as not to link it with Islam.

David Cameron says he's worried "we might lose the public" by changing the name, but assures him he's listening to his case.

As Commons statements go, this is - perhaps unsurprisingly - a pretty long one. Normally, they last about an hour but David Cameron has been on his feet for almost two hours now, and many MPs are still seeking to question him over his case for extending UK airstrikes to Syria. (you can tell how many people still want to ask questions by watching to see them stand up hoping to get called after each response by the PM)

Former Labour shadow chancellor Chris Leslie has described the UN resolution on Syria as "a pivotal moment". Addressing David Cameron a short while ago, Mr Leslie said: