By Katherine Haddon
Britain's parliament looks set to vote in favour of joining the bombing campaign against the Islamic State group in Syria, despite growing doubts among the public and some MPs.
Prime Minister David Cameron kicked off over 10 hours of scheduled debate on Wednesday by urging MPs to "answer the call" from Britain's allies and authorise air strikes against IS targets inside Syria.
"The action we propose is legal, it is necessary and it is the right thing to do to keep our country safe," Cameron said.
But he was forced to fend off calls to apologise, including from opposition Labour leader Jeremy Corbyn, after reportedly telling fellow Conservative MPs at a private meeting not to vote with "a bunch of terrorist sympathisers" against the strikes.
Corbyn, for his part, warned MPs against an "ill-thought rush to war".
Ministers are confident that MPs will ultimately say "yes" in a vote expected at around 2200 GMT (0900 AEDT) while campaigners have promised a new protest outside parliament after a demonstration on Tuesday drew around 4000 people.
The vote comes after US Secretary of State John Kerry urged NATO to intensify the fight against IS.
British support for strikes has dropped sharply in a week according to an opinion poll published on Wednesday, with those in favour down to 48 percent from 59 percent, and those against rising to 31 percent from 21 percent in the YouGov survey for the Times.
Britain is still scarred by the memory of unpopular wars in Afghanistan and Iraq and has played a smaller role in recent foreign military actions, leading to concerns that its global clout is diminishing.
Cameron urged MPs not to allow Iraq to dictate their decision, saying: "This is not 2003. We must not use past mistakes as an excuse for indifference or inaction."
The Prime Minister insists military action is needed to prevent attacks like last month's gun and bomb rampage that killed 130 people in Paris, saying the bombing would be accompanied by a diplomatic push to resolve the Syrian conflict.
The motion up for debate stresses that Britain will not deploy ground combat troops while noting that allies have requested British assistance.
Britain already has eight Tornado fighter jets operating from its military base in Cyprus plus an unknown number of drones involved in strikes on IS targets in Iraq, an operation it joined last year.