Ash Regan's defection to Alba last week should be a teachable moment for the SNP. The party’s immediate response, though, suggests that it will pass unnoticed in a fog of self-delusion.

A healthy and mature organisation would have asked itself some searching questions. Most successful companies do this. Could they have done anything more to keep her? Were there any issues regarding governance and office culture that they ought to know about? Had their former employee felt valued both as a professional and a person?

Enlightened and truly progressive organisations with strong and confident leaders aren’t afraid of uncomfortable answers.

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Why has a former government minister and recent contender for the leadership felt moved to abandon the party in which she’d invested so much emotional and physical energy? Was no-one listening to her oft-stated concerns? Is there any truth to her complaints? These, after all, were very serious and detailed.

Ms Regan’s principal complaint was that the SNP was no longer serious about either fighting for independence or devising anything approaching a workable strategy to secure this. She’d also raised concerns about the influence of the Scottish Greens on the SNP, which she claimed was eroding support for independence.

And when she warned Nicola Sturgeon that the self-ID proposals contained in the Scottish Government’s planned Gender Recognition Reform legislation would result in a massive electoral backlash she was shut down.

In the real world where jobs are on the line such questions coming from someone who had been a senior and highly-regarded figure would have resulted in a crisis meeting among its top tier of management.

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In the last three years the SNP has lost Alex Salmond, its most effective leader; Kenny MacAskill, its most able Justice Secretary and now Ms Regan. They’ve also lost Chris McEleny, the respected former leader of the SNP group on Inverclyde Council. They expelled Angus MacNeil, one of its longest-serving Westminster MPs and front bench spokespersons for saying – more or less – what Ms Regan was saying.

Meanwhile, Fergus Ewing, perhaps one of only two politicians within the SNP with the gravitas to be regarded as a party grandee has been suspended for saying out loud what many within the party have been thinking: that it has been hollowed out and annexed by unserious and not very able people.

No matter how blindly loyal you might be to the SNP the departure of so many people of such high calibre in a few years indicates a dysfunctional organisation that has completely lost its way. It suggests, moreover, that the party is rotten from top to bottom and is barely fit to govern. We know this because all of their concerns and accusations have since been upheld in the court of public opinion.

Indeed, being unserious and not very bright seem to be the chief identifying characteristics of all those who have recently gained high office in the Scottish Government.

This was evident in the way the party conducted itself following Ms Regan’s defection. Humza Yousaf, in a response utterly unworthy of the grand office he holds, said: “If she had principles, she would do the right thing and resign – but I have to say it is no great loss to the SNP.”

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Yet, Mr Yousaf had previously said that Ms Regan “was promoted to Minister for Community Safety which is a tough ministerial brief. She has excelled in that role and worked alongside stakeholders to deliver the best outcomes for all”.  Roddy Dunlop KC, Dean of the Faculty of Advocates, described her in glowing terms when I interviewed him earlier this year. So, was Mr Yousaf lying, or just forgetful?

It was a vindictive and nasty response, characterising the incessant bullying that women inside the SNP have faced in the Nicola Sturgeon/Humza Yousaf era. Taking their lead from the First Minister, a slew of party flunkeys and sycophants piled in publicly to disparage Ms Regan. It typified the poisonous atmosphere that has existed inside the SNP for several years now.

Several sources have confirmed to me that when Ms Regan resigned from the government last year over her concerns about self-ID in the GRR bill she was immediately shunned and marginalised by colleagues who were eager to show the leadership that they were good little toadies.

In the Holyrood canteen this was evident by party MSPs seeking to humiliate her by removing themselves from her presence. I’d been told of something similar happening at Westminster to Joanna Cherry. It’s scarcely believable that people this infantile  get to govern Scotland.

According to Ms Regan (and confirming what many of us had suspected) the decay inside the SNP had begun to corrode its values several years ago. When I interviewed her last week, I asked her when her doubts about Nicola Sturgeon had begun to form.

She said: “I started thinking she wasn’t who I thought she was round about 2018, but immediately you start to think, ‘maybe I’m wrong. Maybe we should just give her the benefit of the doubt for a bit longer. This week though, I’ve been thinking: did she ever have any intention of fighting for independence’?”

Ms Regan also told me that there were around 14 or 15 MSPs who, until the recent party conference, had shared her concerns and spoken openly of rebellion.

The problem for this party is that it has become the establishment in Scotland with its influence and patronage reaching deep into the tributaries and synapses that form civic Scotland. A nod here and wink there from the right people can make your dreams of a decent fitted kitchen and a second home in Argyll come true.

A cohort of mainly young and rootless opportunists have learned that by using the right pronouns and attacking the right people on social media they can rise rapidly through the ranks of the SNP and find themselves on list of preferred candidates. In geopolitical terms what Ms Sturgeon has bequeathed to her successor is akin to pre-revolutionary Cuba – spent and wasted –  when it had become a playground for the mafia  If this is to be a teachable moment for Mr Yousaf then he must make some hard choices and very quickly. His predecessor and her WhatsApp cabinet have virtually destroyed any prospect of an independent Scotland. All that’s left is to regain the trust of voters at the next Scottish election.

He must immediately ditch the Scottish Greens and then seek an electoral rapprochement with Alba. And he must empty his cabinet and his executive advisory and start all over again with people of proven ability who genuinely want independence.