David Cameron has been accused of resorting to a “desperate slur” in the debate on Syria air strikes, after he described Jeremy Corbyn and other opponents of action as “terrorist sympathisers”.

The Opposition leader’s office has hit out angrily after the Prime Minister’s comments, made during a private meeting of Tory MPs the evening before Wednesday’s crucial debate and vote on whether Britain will go to war in Syria.

Addressing the influential 1922 Committee, Mr Cameron was reported to have urged them to vote in favour of strikes, saying he needed all Conservatives on side to ensure a majority in the Commons.

And according to MPs who were present, he told them: “You should not be walking through the lobbies with Jeremy Corbyn and a bunch of terrorist sympathisers.”

Cameron agrees Syria question

John Baron, an ex-army Tory MP and Foreign Affairs Committee member who is vocally opposed to action, criticised his own leader when asked on BBC’s Newsnight how he felt about being described as a “terrorist sympathiser”.

“I was a platoon commander in Northern Ireland and I do think we must not resort to such language,” he said.

“Instead we should look at the actual evidence before us. There is clearly a lack of ground force to take Daesh on and that is one of the key issues we have got to address.”

In pictures: Syria air strikes (2014) Show all 20 1 /20 In pictures: Syria air strikes (2014) In pictures: Syria air strikes (2014) Syria Syrian citizens check a damaged house that targeted by the coalition airstrikes, in the village of Kfar Derian, a base for the al-Qaida-linked Nusra Front, a rival of the Isis group, between the northern province of Aleppo and Idlib In pictures: Syria air strikes (2014) Syria A Syrian boy (L) looking at a destroyed car that activists say was targeted by the coalition airstrikes, in the village of Kfar Derian, a base for the al-Qaida-linked Nusra Front, a rival of the Islamic State group, between the northern province of Aleppo and Idlib In pictures: Syria air strikes (2014) Syria Parts of a missile that activists say was fired by coalition airstrikes, in the village of Kfar Derian, a base for the al-Qaida-linked Nusra Front, a rival of the Isis group, between the northern province of Aleppo and Idlib In pictures: Syria air strikes (2014) Syria Tthe guided-missile destroyer USS Arleigh Burke (DDG 51) launching Tomahawk cruise missiles against Isis targets In pictures: Syria air strikes (2014) Syria The USS Arleigh Burke (DDG 51) launches a Tomahawk cruise missiles in the Red Sea, to conduct strike missions against Isis group targets in Syria In pictures: Syria air strikes (2014) Syria The guided-missile cruiser USS Philippine Sea (CG 58) launching a Tomahawk cruise missile against Isis targets in Syria, as seen from the aircraft carrier USS George H.W. Bush (CVN 77) in the Arabian Gulf In pictures: Syria air strikes (2014) Syria US navy sailors standing watch on the bridge while Tomahawk cruise missiles are launched against Isis targets in Syria, aboard the guided-missile cruiser USS Philippine Sea (CG 58), in the Arabian Gulf In pictures: Syria air strikes (2014) Syria An F/A-18C Hornet, attached to Strike Fighter Squadron (VFA) 87 prepares to launch from the flight deck of the aircraft carrier USS George H.W. Bush (CVN 77) in the Arabian Gulf, to conduct strike missions against Isis group targets AFP/Robert Burck In pictures: Syria air strikes (2014) Syria The US-led airstrikes in Syria against Isis targets in and around the city of Raqqa In pictures: Syria air strikes (2014) Syria A fighter from the Isis group holds a piece of what the IS is saying is a US drone that crashed into a communications tower in the Syrian city of Raqqa In pictures: Syria air strikes (2014) Syria Fighters from the Isis organisation pray at the spot where the jihadist group said a US drone crashed into a communications tower in the Syrian city of Raqqa In pictures: Syria air strikes (2014) Syria Fighters from the Isis group load a van with parts that they said was a US drone that crashed into a communications tower in the Syrian city of Raqqa In pictures: Syria air strikes (2014) Syria Fighters from the Isis group load a van with parts that they said was a US drone that crashed into a communications tower in Raqqa In pictures: Syria air strikes (2014) Syria Fighters from the Isis group gesture as they load a van with parts that they said was a US drone that crashed into a communications tower in Raqqa. A US-led coalition on carried out its first air strikes and missile attacks against jihadist positions in Syria, with Damascus saying it had been informed by Washington before the operation began In pictures: Syria air strikes (2014) Syria A Syrian man rides his bike past a communications tower that was destroyed after a US drone crashed into it, according to fighters with the Isis group, in the Syrian city of Raqqa In pictures: Syria air strikes (2014) Syria People inspect a shop damaged after what Isis militants say was a U.S. drone crashed into a communication station nearby in Raqqa In pictures: Syria air strikes (2014) Syria A man holds the remains of what Isis militants say was a U.S. drone which crashed in Raqqa In pictures: Syria air strikes (2014) Syria Resident gather in the back of a van the remains of what Isis militants say was a drone which crashed in Raqqa In pictures: Syria air strikes (2014) Syria A man inspects the remains of what Isismilitants say was a U.S. drone which crashed into a communication tower in Raqqa In pictures: Syria air strikes (2014) Syria A man inspects the remains of what Isis militants say was a U.S. drone which crashed in Raqqa

Labour has called for Mr Cameron to apologise for his comments – in stark contrast with the measured statements he has made in urging MPs towards voting for air strikes in recent days.

A YouGov poll for The Times found public opinion moving against air strikes - with the proportion in favour dropping from 59 per cent to 48 per cent and those against rising from 20 per cent to 31 per cent with undecideds unchanged on 21 per cent.

And writing for the Guardian, Mr Corybn said the case for strikes was “coming apart at the seams” - notable the claim of 70,000 moderate forces on the ground to take advantage of air strikes against IS. “He knows that opposition to his ill-thought-out rush to war is growing,” he said.

Last night, Mr Corbyn’s spokesman described Mr Cameron’s comments as “a contemptible and desperate slur which demeans his office”.

“He clearly realises he has failed to make a convincing case for military action and that opinion is shifting away from him,” he said.