Fergus Ewing versus Lorna Slater is a test of the SNP's commitment to being a 'national' movement – Brian Wilson

Nationalism depends on being the broadest of political churches since it is shared identity that holds such movements together

It was deeply ironic that, on the day news of Winnie Ewing’s death emerged, Humza Yousaf was humming and hawing about whether to withdraw the SNP whip from her son for breaching party discipline. “Greens in, Ewing out” is not a great backdrop to the tributes that will flow this weekend. Perhaps more thoughtful members of the nationalist hierarchy will address themselves to an inconvenient question – where would Winnie have stood on the issues over which Fergus has broken ranks?

Gender recognition reform? Highly protected marine areas (HPMAs)? The deposit return scheme? I would bet a pound to a groat she would have been as sceptical as her son about the political wisdom driving any of the above. Perhaps that offers an opportunity for Mr Yousaf to press the pause button, reflect and respect the possibility that Fergus is right and the policies are wrong.

None of this has anything to do with independence. Mr Ewing is as much committed to that objective as any of those who would cast him out. From my own perspective, it is possible for him to be wrong on that issue and right about all the others. And he would say the same in reverse about me.

The trap the SNP has set for itself is to make every policy which has absolutely nothing to do with the constitution a loyalty test. Nationalism depends, by definition, on being the broadest of political churches since it is shared identity that holds it together, neither right nor left. That is both its electoral strength and its ideological weakness.

Yet the demand for party unity forces its representatives to support policies which are irrelevant to that binding force. It has taken Mr Ewing to call out that basic flaw which has, in its current manifestation, opened the door to Green extremism and faddist opportunism, all under cover of the shared constitutional objective.

When he tore up the HPMA document, Fergus specifically referred to his mother having spent 40 years defending Highlands and Islands fishermen. As an MEP, she used to speak rather proprietorially about “my fishermen” and none of them objected. How on earth could Fergus have honourably reconciled that history with the Draconian HPMA plans?

His hanging offence this week was to not express confidence in Scottish Green minister Lorna Slater. Far from being a clincher for making him an outcast, this may confirm Mr Ewing as the only honest SNP representative at Holyrood since, in truth, it is difficult to believe that more than a few of them share the confidence that they were instructed to proclaim.

Mr Ewing probably knows more about the origins and pitfalls of the deposit return scheme than any other politician at Holyrood. He was around as Cabinet Secretary for the Rural Economy when it was conceived of and has been expressing his doubts ever since he had the freedom to do so. He should have been listened to as an insider, rather than scorned as a recalcitrant rebel.

The bills are now beginning to land and that will be the true determinant of where responsibility lies. For starters, the Scottish National Investment Bank appears reconciled to waving goodbye to £9 million of public money, having been led – presumably under ministerial guidance or even insistence – into investing in Circularity Scotland.

Amidst all her amateur theatricals, Ms Slater has not yet explained why the unambiguous insistence from Circularity Scotland that the scheme could go ahead next March without the inclusion of glass was ignored. That was a lifeline thrown to Ms Slater if, indeed, the scheme was otherwise ready to go and her aim was delivery rather than confrontation.

Fulminating about the wickedness of the UK Government and alleging its improbable determination to “sabotage” the scheme cuts very little ice, except among the most wilfully delusional. This is because almost every other voice they hear tells them a different story and even obvious questions about how it was going to work remain unanswered.

The charge is that the Scottish Government allowed Ms Slater to plough on in full knowledge they were on a high-risk collision course. Alongside great swathes of industry, Mr Ewing told them so repeatedly. They knew about the Internal Market Act two years ago but made no application until March, only after an official warned that without “a fast-track commitment to an exemption within the next week… we run a very serious risk of compromising our go-live date”.

I repeat: “A fast-track commitment to an exemption within the next week.” Is that the way to run a major piece of legislation in which hundreds of millions of pounds have been invested on the basis of assurances from government? In truth, no application had been made because there was no settled scheme to base it on with hundreds of questions still unanswered and the rules changing by the week.

All this will come out in the wash, once compensation claims start landing. I would be particularly interested to learn what else the civil servants, who are supposed to protect us from the fiscal recklessness of ministers, told Ms Slater at each stage. Why not volunteer that information now, Mr Yousaf, as evidence of why confidence in the minister is justified?

Since being liberated from office, Mr Ewing has been the model of what a troublesome backbencher should be. All other parties live with them. The stifling uniformity that the SNP demands leave its MSPs as hostages to policies and, in Ms Slater’s case, performances which are, in large part, the consequences of a coalition nobody ever voted to instal.

Now the shock of dissent has finally emerged, it has been met with over-reaction rather than even the slightest introspection. I doubt if it is in the spirit of the Ewing dynasty to back down that easily.