The question of whether Britain should launch air strikes against Syria is a dangerously tricky and finely balanced one – which is why the nation and the Labour party is divided over it. But the job of Jeremy Corbyn, as the leader of the official opposition, was to show leadership on the issue and take his party with him. By allowing his MPs a free vote, he has failed to do so and as a result is seriously weakened. Indeed, his leadership may now be fatally undermined.

On the principle at the heart of the argument, no one has ever doubted Mr Corbyn’s position. He is a pacifist and a former chairman of the Stop the War coalition and it was never likely that he would support the UK’s involvement in another conflict, especially with Iraq and Afghanistan still casting their shadows over his party.

Mr Corbyn’s decision to oppose air strikes was also perfectly understandable in the face of the arguments for war advanced by the Prime Minister. David Cameron says we must launch air strikes because IS pose a threat to the British people, and insists that are 70,000 anti-Assad fighters on the ground who could be used to finish the job.

But Mr Corbyn has asked the questions that many others have been asking, including this newspaper. Military action could increase the risk of another terrorist attack in the UK, not decrease it, and would British involvement in a campaign that has already seen a coalition of nations bombing Syria for many months add anything of substance? There is also the question of ground troops – every senior military expert says they will be needed to win the war and yet Mr Cameron says the UK will not provide them. So who will?

All of these questions – and the fact that Mr Cameron has not provided completely convincing answers to them - have led Mr Corbyn to oppose air strikes, and we know most of his membership is behind him. The problem, though, is that much of his parliamentary party, including many in the shadow cabinet, are not and support air strikes, which has left Mr Corbyn agonising over what to do. Allow a free vote and he would effectively hand a win to Mr Cameron and military action will go ahead; insist on whipping his MPs and he would risk mass resignations from his cabinet.

In the end, he chose a free vote, but it is the wrong decision for him and his party. Allowing a free vote might look like the tactically wise decision in the short term because it avoids the risk of front-bench resignations, but it puts party management above the responsibilities of opposition and means that the official opposition does not have a united position on the most important issue of the parliament so far.

Mr Corbyn says opposition to air strikes is still official party policy but that is an attempt to salvage a situation that is essentially damage limitation. The fact that the Labour party cannot produce a united front on something as important as whether or not the country goes to war can only be profoundly damaging to the party, and by extension to its leader.