What does the Salmond v Sturgeon feud mean for the future of the union?

When old foes clash, things can turn nasty. But the goriest of all battles are those waged when former comrades go to war. This rule of politics has a vivid case study in the extraordinary duel being fought between Alex Salmond, who led the Scottish National party for 20 years, and Nicola Sturgeon, who was his deputy for 10 of them before becoming leader and first minister nearly seven years ago.

I’ve had a ringside seat for many a political feud. Heath versus Thatcher. Thatcher versus Major. Blair versus Brown. Brown versus Mandelson. Osborne versus May. Cameron versus Cummings. Cummings versus just about everybody. I thought I could no longer be shocked, but none of the above were as lurid as the bitter struggle that has erupted in Edinburgh. Mr Salmond accuses senior figures in the party he once led of a multi-tentacled conspiracy to destroy his reputation. In a 26-page document submitted to an inquiry by the Holyrood parliament, he makes the sensationally grave accusation that Ms Sturgeon’s inner circle ran a “deliberate, prolonged, malicious and concerted effort” to discredit him, “even to the extent of having me imprisoned”.

On his account, the plotting involved Ms Sturgeon’s chief of staff and the party’s chief executive, Peter Murrell, who used to be one of Mr Salmond’s under-strappers. In the tight world of the SNP, Mr Murrell also happens to be Ms Sturgeon’s husband. This is like Carrie Symonds being chairwoman of the Tory party or Victoria Starmer being general secretary of the Labour party. The Salmond-Sturgeon feud is the more vicious because it involves a small circle of alpha personalities who have a long and intimate history with one another.

He further charges Ms Sturgeon with misleading the Scottish parliament about her role in, and knowledge of, her government’s investigation into complaints of sexual misconduct made against him. That probe was subsequently ruled “unlawful” and “tainted with apparent bias” by a judicial review.

It is not just Ms Sturgeon’s integrity and truthfulness that is on trial here. Her predecessor is also loquacious about failures in the leadership of Scotland’s civil service and prosecuting authorities. “Concealing evidence from the courts matters,” he declared in testimony on Friday. “Suppressing evidence from parliamentary committees matters.” This is spicy stuff coming from the country’s former first minister. If he is to be believed, Scotland under the SNP is not so much a mature democracy as a cold weather version of a banana republic.

Ms Sturgeon and her allies furiously counter that Mr Salmond, a man she first met as a teenage activist, is peddling baseless conspiracy theories and trying to sacrifice the reputation of Scotland’s institutions on the altar of his own ego. The SNP has been dominant in Scotland for 14 years and this affair illustrates that it is no less vulnerable than any other party to the dangers associated with being in power for such a prolonged stretch. If anything, the risks that come with one-party hegemony are amplified in a country with a population similar in size to that of Yorkshire and where everyone in public life knows everyone else. Critics have long complained that the SNP runs a highly centralised regime that has a with-us-or-against-us mindset hostile to anyone who does not share the party’s view of what it means to be a patriotic Scot. One veteran of Scottish politics says the country has become “a cold house” for anyone working in the public sector or for civic organisations who do not entirely adhere to the SNP’s worldview. It becomes harder for civil servants to maintain their due impartiality when there seems a vanishingly slight chance of anyone other than the SNP being in charge. You don’t have to think Mr Salmond a good man or to be persuaded by every one of his allegations to see force in his case that the boundaries between government business and party interests have become blurred during the SNP’s long reign.

Another problem associated with governments that don’t have much fear of electoral defeat is that they become factionalised. There is a factionalist dimension to this feud. The former leader commands the fealty of a section of the SNP who think Ms Sturgeon hasn’t established a credible route to securing another independence referendum. The SNP have proved formidable campaigners, but much more mediocre as governors. Their most creative term in office was probably their first, a minority administration when Mr Salmond was in charge. They might be a more self-questioning government if they thought they faced a serious electoral challenge. They don’t. The Tories are the official opposition, but something extraordinary will have to happen for them ever to lead the government there. Ten weeks out from the May elections to the parliament, Labour has just chosen Anas Sarwar as its new leader north of the border. He takes the helm with his party a poor third in the polls. Scottish Labour has burnt through seven previous leaders since it lost power at Holyrood in 2007 – and that’s not including all those who were “acting leader”.

Until very recently, the SNP looked to be cruising towards yet another electoral triumph. The imposition of a Brexit that most Scots didn’t want by a Tory prime minister liked by even fewer of them have been rocket boosters. Even Scottish Tories acknowledge that Boris Johnson could not have been more perfectly designed to aggravate Scots if he had been designed in an SNP lab.

The question now animating strategists of all parties is how much the Salmond-Sturgeon struggle will hurt the SNP with the voters. If the traditional rules still apply, we would expect it to suffer severely from such a toxic battle between the two largest figures in Scotland’s independence movement. This ugly business punctures the SNP’s habitual air of moral superiority over the pro-union parties. While he says he would not himself call Scotland a “failed state”, Mr Salmond’s barrage against the institutions of Scottish democracy and justice is not exactly helpful to the case for independence. The titanic quarrel between the two people who have dominated Scotland for 14 years might be a prompt for more of the electorate to inquire into how well they have been governed over that long stretch.

Even if past supporters of the SNP are reluctant to switch to other parties, some of them might register their distaste by staying at home rather than going out to vote. Participation in the last elections for Holyrood was an unimpressive 56%. Were turnout to fall below 50% this May, you can expect to hear Tories contending that this deprives the SNP of any right to claim a mandate for another referendum on independence even if they win a majority.

It is not just the Conservatives; it is all the pro-union parties, who will be hoping that this affair marks the long-awaited moment when SNP hegemony begins to crack and its support starts to crumble. Truth be told, there’s not much evidence for that yet. Polling suggests there has been some erosion to Ms Sturgeon’s standing with Scottish voters and a dent in support for independence, but she is still far more popular than any of her rivals.

In recent years, and in many different places, we have witnessed a significant change in how electorates choose and judge their rulers. Fewer voters assess leaders on traditional criteria, such as whether they are competent and dynamic administrators or decent and honest people. A growing number of analysts contend persuasively that many more voters now make their political choices based on identity. Their most important yardstick for supporting a politician is whether or not he or she represents their tribe. Donald Trump won’t have read any of these books, but he backed their thesis when he made the claim that he was so confident of his support base that he could stand in the middle of New York’s Fifth Avenue “and shoot somebody and I wouldn’t lose any votes”.

The Salmond-Sturgeon knife fight may not lose the SNP as many votes as opponents might hope among those Scots for whom independence takes precedence over any other consideration. That is one reason for Number 10 to contain its glee about what is unfolding in Edinburgh. Boris Johnson, much as he must be tempted to comment, would be wise to stay out of this affair. Even a badly damaged SNP will be a great deal more popular in Scotland than he can ever hope to be.

• Andrew Rawnsley is Chief Political Commentator of the Observer