Labour’s now notorious shadow cabinet meeting on Syria started with Jeremy Corbyn briefly reading from a piece of paper. More than once the ­Labour leader was asked to speak up by those sitting round the long wooden table.

According to one source, he said little thereafter during a 90-minute discussion about UK foreign and national security policy. His relative silence, and reluctance to hold confrontational arguments, reflect his consensual personality and are a tribute to his collective style of leadership, say his allies.

To others, it is a cause of intense frustration. One shadow cabinet member complains: “He had no ability to chair the meeting, shape a discussion, sum up a debate or anything. He cannot propose or defend an argument forensically. He never really expresses his views in the shadow cabinet. In meetings outside shadow cabinet, he largely leaves it to his advisers.”

These criticisms are from a shadow cabinet member who has no plan to resign – “what on earth would be the point of that?” – and who, like the shadow foreign secretary, Hilary Benn, does not object to Corbyn issuing a surprise letter to the party saying he is determined to oppose airstrikes. This source argues: “He is the leader of the party. If anything I wish he would express his views more.”

Equally, Corbyn’s supporters argue it is perfectly justifiable for the leader to set out his view, and for him to try to rally support this weekend among MPs and constituency parties before next week’s critical meetings of the shadow cabinet and Labour MPs.

Corbyn believes he has more support in the parliamentary party than in the shadow cabinet, and one poll, conducted by YouGov, suggests a majority of party members do oppose airstrikes, even if Labour voters take a different view. That constituency majority view, if it exists, now intends to makes its views known this weekend at rallies, party events and in social media.

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But some in the shadow cabinet take a less charitable view of Corbyn’s behaviour, saying it is part of a pattern since he became leader that has contributed to a near breakdown in trust. They complain Corbyn’s most senior office staff were personally involved in drafting the letters pressing MPs to oppose airstrikes. Corbyn’s critics argue that Momentum, the independent grassroots group supporting the leader, is now being organised by MPs loyal to Corbyn and indeed the leader’s office, all part of a quite visible plan to take control of the party machine, appoint key people and strengthen the role of the national executive.

The danger is that the passionately conducted dispute over Syria is spiralling out of control and becoming a surrogate for the simmering battle for Labour’s soul. The demand for a three-line whip in favour of airstrikes, if rejected by Corbyn, could then become the point at which frontbench resignations on a point of principle follow.

The irony is that, behind this bitter power struggle, the highest echelons of the party have been trying to conduct a serious debate on Syria that transcends slogans or the resettling of scores from the Iraq war.

One present at the shadow cabinet meeting on Thursday says: “Yes, there was a spat between Diane Abbott and Lucy Powell, and Diane should not have mimicked Lucy’s accent, but overall there was a very serious discussion and it was completely clear that a majority are in favour of airstrikes. At the moment there are four against and a similar number undecided.”

Four points seemed at issue in this discussion. The identity, loyalty and location of any ground troops to take over land occupied by Islamic State; the prospects of the wider peace process including an exit strategy; the real value of UK airstrikes in disrupting Isis; and finally, but less prominently, the legal authority for airstrikes.

Corbyn’s allies challenge the joint intelligence committee claim that there are 70,000 credible “moderate” Free Syrian Army soldiers. In Labour’s private discussions, it has been argued the FSA troops are largely fighting the president, Bashar al-Assad, closer to Aleppo and Damascus and are not arrayed against Isis in north-east Syria, a point Corbyn himself referenced in his response to David Cameron’s Commons statement.

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This critique is challenged by those who point out many British troops were stationed in East Anglia before D-day but were moved. The counter-argument to this is that in the absence of a wider peace deal, these moderate forces are not going to move to the frontline against Isis, meaning in practice the ground force will be constituted by Kurds, or Islamist groups such as Jaysh al-Islam and Ahrar al-Sham. But that puts a heavy onus on nurturing the deeply incomplete UN-led Vienna peace process, designed to form a new Syrian coalition government and hold elections in 18 months. A new unity government could take on Isis effectively.

It is clear from discussions with shadow cabinet members that those who support airstrikes acknowledge the deficiencies of the peace process, but still believe in the interim the case for airstrikes is compelling.

A need to show solidarity with the French plays a role. But the majority of the shadow cabinet, influenced by briefings on intelligence, believe British airstrikes can be effective in disrupting the command and communications of Isis headquarters in Raqqa, and so bolster UK security. As for the risk of terrorist reprisals, the shadow cabinet has been told by the government that Britain is already a first tier target.

The legal basis for war has been addressed by the shadow solicitor general, Catherine McKinnell, and in the past challenged by Abbott. The UN security council has not passed a chapter 11 resolution authorising force, although a lesser resolution has been passed. So has the Labour conference demand for unambiguous UN support for airstrikes been met? In the view of shadow cabinet legal sources, airstrikes amount to self-defence.

Perhaps Labour has now gone beyond fine legal arguments or dispassionate evaluation of the best solution to the tragedy engulfing Syria.Other agendas have taken hold. The rational, if deeply unsatisfactory, solution is for the shadow cabinet to admit it is split, and give its MPs a free vote. It would be rare for a political party to fail to reach a collective view on such a vital matter of national security. Next week will reveal whether such an messy outcome would satisfy Cameron and the electorate.