Labour

Earlier predictions that 100 or more Labour MPs would back bombing — the same number as rebelled against Tony Blair to oppose the Iraq war in 2003 — are looking inaccurate.

The whips office estimates that shadow foreign secretary Hilary Benn will lead between 30 to 50 Labour hawks into the lobby behind Dave Cameron.

Deputy leader Tom Watson is also expected to be in the group consisting mainly of Blairites like Liz Kendall, Chris Leslie and John Woodcock, but also party grandees such as Alan Johnson and Margaret Beckett. 

Despite a free vote, most MPs and members of the shadow cabinet have been unconvinced of Mr Cameron’s case and stood with Jeremy Corbyn against air strikes.

Tories

Not only does David Cameron not trust the consciences of his MPs enough to call a free vote, he has told them that anyone walking through the No lobby with Jeremy Corbyn is a “terrorist sympathiser.”

He cowed some influential backbenchers who helped defeat his bid to bomb Syria in 2013, such as Dr Sarah Wollaston and foreign affairs select committee chairman Crispin Blunt. But John Baron, also a member of that committee, and defence select committee chairman Julian Lewis remain unconvinced.

Their opposition reflected the weakness of Mr Cameron’s case but won't be enough to stop him winning the vote.

Scottish National Party

Leader Nicola Sturgeon has been keen that her historically anti-war party was not taking a pacifist position, saying last week that she was prepared to listen to the PM’s case.

Westminster leader Angus Robertson was not though convinced by the high-level security briefing that has been spooking so many others and all 54 of the party’s MPs are expected to oppose bombing.

Lib Dems

In a bid to erase his party’s toxic recent history of propping up the Tories in coalition, new leader Tim Farron has presented himself as a centre-left populist in the mould of Charles Kennedy, who offered principled opposition to the Iraq war.

So it was a surprise when Farron announced on the eve of the vote that the eight surviving Lib Dem MPs would back bombing. Justifying the decision, he echoed Nick Clegg's coalition excuse, saying it is “in the national interest." 

Anti-war minor parties

Mr Cameron’s snap vote has forced Plaid Cymru to cancel their Christmas party. Former Plaid MP Adam Price led the campaign to impeach Tony Blair over the Iraq war and their three MPs, along with Green Caroline Lucas, with whom they co-operate closely, offered principled opposition to the latest British intervention in the Middle East.

Three SDLP MPs from the Northern Ireland will bolster their numbers. 

Pro-war minor parties

Unfortunately their numbers are exceeded by 10 unionist MPs, eight from the DUP and two from the UUP, who could help Mr Cameron win a vote even without the support of Labour MPs.

Ukip

Nigel Farage has come out against bombing, but the party’s sole MP Douglas Carswell was awarded the “rebel of the year” award on the eve of the vote. A stunning achievement in a group of one that made it impossible to predict how the maverick will vote.

The tally 

For bombing: Around 320 Tories MPs, 30-50 Labour, 8 Lib Dems, 8 DUP, 2 UUP — Between 368 and 388

Against bombing: Between 180-201 Labour MPs, 54 SNP, 10, Tories, 3 Plaid, 3 SDLP, 1 Green — Between 251 and 271

Likely outcome: Majority of between 97 and 137