Jeremy Corbyn has written to Labour MPs today to say he cannot support airstrikes against Isis in Syria.

The Labour Leader wrote that he remains unconvinced that they would make Britain safer or contribute toward a comprehensive negotiated political settlement in Syria. His letter comes after David Cameron tried to persuade MPs of the case for military action this morning.

Corbyn’s stance puts him at odds with senior members of the Shadow Cabinet, which met to discussed the issue after the Prime Minister’s statement. The Shadow Foreign Secretary, Hilary Benn, told the meeting that he thought the case for airstrikes was “compelling”.

Afterwards Benn told the BBC that the threat from Isis against the British people was “very real” and that it is “very important that we now take action to end that threat.”

Corbyn is hopeful that the Shadow Cabinet will be able to agree a common position when it meets again on Monday ahead of a Commons vote on airstrikes next week. LabourList understands he is also open-minded about giving Labour MPs a free vote on the issue, although that is not his preferred option or something he regards as straightforward.

Corbyn’s letter says that the Labour’s “first priority must be the security of Britain and the safety of the British people” and that the issue is whether the Prime Minister’s proposals “strengthens, or undermines, our national security.”

“I do not believe that the PM today made a convincing case that extending UK bombing to Syria would meet that crucial test. Nor did it satisfactorily answer the questions raised by us and the Foreign Affairs Committee.

“In particular, the PM did not set out a coherent strategy, coordinated through the UN for the defeat of ISIS. Nor has he been able to explain what a credible and acceptable ground forces could retake and hold territory freed from ISIS control by an intensified air campaign.

“In my view, the PM has been unable to explain the contribution of additional UK bombing to a comprehensive negotiated political settlement of the Syrian civil war, or its likely impact on the threat of terrorist attacks in the UK.

“For these, and other reasons, I do not believe the PM’s current proposal for air strikes in Syria will protect our security and therefore cannot support it.”

Corbyn is likely to speak out against military action when he visits Newcastle this evening and Oldham tomorrow. And the pro-Corbyn pressure group Momentum has circulated a draft letter against airstrikes for its supporters to send to Labour MPs. Unite’s General Secretary, Len McCluskey, has also backed Corbyn’s stance, saying that “the Prime Minister has failed to make a case for bombing Syria.”