Amid the wreckage of the EU referendum campaign, Labour figures from the shadow Cabinet to the grassroots are now looking at Monday’s meeting of MPs as the crunch moment for the future of Jeremy Corbyn’s leadership.

A discussion of the no-confidence motion at Monday evening’s meeting is likely to prompt a secret ballot on the leader and this could be held as soon as Tuesday.

Both sides of the parliamentary party are uncertain, however, of the impact of a non-binding vote. And supporters of Corbyn can, as always, point to their man’s popularity among the membership in polls taken relatively recently (although before Thursday’s events).

But beyond the PLP vote there is another crucial question: what if Corbyn struggles to command the support of his own shadow Cabinet? That, then, could deliver a near-fatal blow. The moderates hope Corbyn would then be persuaded to go of his own accord rather than sign up for another four years of herding a rebellious PLP.

This is why shadow Cabinet ministers and “moderate” backbenchers are this weekend engaged in a hectic round of conversations as to their stance on Monday.

But how likely is it? Sources close to the leader are adamant that he retains the support his frontbench.

Yesterday’s shadow Cabinet meeting took the form of a near-three hour post mortem on Labour’s doomed EU campaign. The sceptical members of the top team are angry that, having put aside their doubts to serve under a winner in September, they are now shackled to a man who has lost an election which was eminently winnable.

They are also worried about the impact of a new Tory leader, particularly if it turns out to be Boris Johnson, and the prospect of fighting and losing a general election against a fresh prime minister before the end of the year. They have been stung by the flow of Labour heartland support to the Leave campaign and view it with emotions ranging from concern to outright panic.

So, as the phone lines buzz over the weekend, backbenchers are telling shadow Cabinet ministers that just as they agreed to serve out of a desire to act in the broader interests of the party in September – giving a new leader the support he needed – now they must act with the same intentions by withdrawing that support in favour of someone who can re-connect the party with eurosceptic grassroots Labour members and supporters.

The issue, yet again for our party, is immigration. The vote for Brexit was driven in part by anger over immigration and the timing of Corbyn’s admission last weekend that there could be no upper limit on immigration while Britain was signed up to free movement of labour left some MPs immensely frustrated.

This is the difference from September, because now backbenchers are pointing to evidence of an electoral disconnect between the top of the party and its supporters in the country.

What is clear is that immigration is not the terrain on which Corbyn would have chosen a showdown with his rebellious MPs. He will, however, say more on this subject in the coming days.

As MPs debate among themselves this weekend, today’s write-ups of a tumultuous week are notable for two reasons.

Firstly, union leaders have come out en masse for Corbyn, telling LabourList “the last thing Labour needs is a manufactured leadership row of its own in the midst of this crisis”.

Secondly, there has not so far been a show of support from the shadow Cabinet. Contrast this with the eruptions of the PLP during the Blair and Brown years, when ministers would be dispatched to television studios to pledge their backing for the leader.

Now that does not mean Corbyn is a goner. The shifting loyalties and messy logistics of Westminster are always far more complex than that. And Corbyn’s camp is relatively relaxed about the PLP motion, which they will have been expecting for some time. And they will continue to feel very confident the leader could command support among the members. But, before then, it seems likely the shadow Cabinet will have a huge say in what happens next.