TENSE, passionate, at times acrimonious but always insightful, the start of the House of Commons marathon Syria debate has been high political drama.

David Cameron’s ill-judged remarks to the Tory 1922 Committee in which he branded opposition politicians opposing airstrikes “a bunch of terrorist sympathisers” got in the way of the early exchanges.

MP after MP stood up to interrupt the Prime Minister to get him to withdraw and apologise for his controversial comment, branded “offensive, dangerous and untrue” by Labour’s Emily Thornberry.

An indignant Alex Salmond, the former First Minister, told the PM that he had examined the list of 110 MPs, who had supported the amendment opposing airstrikes, and could “not identify a single terrorist sympathiser among that list. Will you now apologise for your deeply insulting remarks?"

But it was clear the Conservative leader was not for budging and effectively told the House – nothing to see here, let’s “move on”.

But at first, it wouldn’t. As the questions continued, he told MPs, to much opposition barracking, that he “respected” people who disagreed with him and that “there's honour in voting for, there's honour in voting against".

Labour backbencher Gisela Stuart offered Mr Cameron some “motherly advice” that he would gain much respect if he apologised and Jeremy Corbyn accused him of demeaning the office of Prime Minister by his remarks, offering him another chance to say sorry.

But the PM sat impassively, arms-folded, on the Government frontbench.

Despite some MPs seeking to prolong the premier’s embarrassment, the House gradually did move on and concentrated on the pros and cons of extending airstrikes given that some 157 MPs had put their names down to speak before the 10pm vote.

Mr Cameron’s central argument was that Britain would be safer by seeking to degrade IS – now apparently officially dubbed Daesh – to prevent a terror attack at home in the near future.

The rhetoric was strong. He branded IS “medieval monsters”, warning MPs that they should be under no illusion that “these terrorists are plotting to kill us and to radicalise our children right now".

He also sought to address the point that, if there were a terror attack after a vote for airstrikes, that the vote would be somehow responsible for the attack.

He declared: “I do not believe that that will be the case,” pointing out how IS had been trying to attack the UK for the past year and seven different plots had been foiled.  

One key point – ground troops – again appeared to fail in reassuring MPs’ concerns.

Indeed, after repeating the 70,000 moderate forces figure again, Mr Cameron acknowledged himself that these were not “ideal partners” but could in some form be useful and play a role in the future of Syria. It was not the PM’s strongest point and many MPs’ heads were seen shaking as he made it.

On the issue of civilian casualties, the Tory leader stressed how in 15 months of UK forces bombing Iraq, there had not been a single report of a civilian casualty.

He pointed out that after Tikrit in Iraq was retaken from IS, some 70 per cent of locals returned.

Tory MP Nadim Zahawi, who recently visited Iraq, intervened to note that people in Baghdad wanted the UK to extend bombings otherwise IS would regroup and begin attacking them again.

In his opening statement, Mr Corbyn spoke calmly but firmly, dismissing the plan for airstrikes as “ill thought through” and which would "almost inevitably lead to the deaths of innocents".

The Labour leader warned of "mission creep" and the "real possibility" of British troops being sent to Syria should MPs support the extension of airstrikes.

One of his strongest lines was how the “spectre” of Afghanistan, Iraq and Libya, loomed over the debate on Syria, arguing these had increased terrorism not decreased it.

“To oppose another reckless and half-baked intervention isn't pacifism. It's hard-headed common sense,” he declared.

The Labour leader argued that the emphasis should not be on more military action but on putting all efforts on diplomatic efforts to end the civil war in Syria.

But Tory backbenchers who intervened sought to stress the imminence of the terrorist threat to Britain and the urgent need to degrade IS’s capability as quickly as possible.

Mr Corbyn came under some pressure when he would not directly answer Conservative calls on whether or not he supported the current military action in Iraq, which is claimed by Ministers to have proved successful in pushing back IS.

In the chamber as Mr Corbyn refused to take Tory interventions as Conservative MPs shouted: “Answer!”

Tory backbencher Jacob Rees-Mogg cannily used a point of order to ask again if the Labour leader supported the UK’s current airstrikes in Iraq.

After the Labour leader again brushed aside the question, a senior aide later acknowledged the Opposition supported the current policy in Iraq but made clear it believed it was “not working” and needed to be looked at again.

Angus Robertson for the SNP, who has the comfort of knowing all his MPs will vote the same way in opposing military action, stressed how doing nothing in face of the threat from IS was not an option.

But there was “no shortage” of allies bombing the terrorists and the Nationalist leader again alighted on the 70,000 ground forces figure and asked how many were really moderate and how many were fundamentalists.

Tory MP Richard Benyon accused him of making a “nitpicking, quibbling point” and “dancing on the head of a pin”.

He told MPs: "There are these people, we have to trust them, they are not on Assad's side and they are not on Isil's side; we need to work with them."

After the initial exchanges, a senior Labour aide made the most insightful comment, saying that the Government could “expect to win the vote but has lost the argument”.