In a rule of thumb attributed to Alastair Campbell, when a politician “becomes the story” they’ve only days to clear themselves before they must depart the scene to prevent lasting damage to their party. That was before Alex Salmond became the story.

The former First Minister is the most formidable fighter in politics and will not to go quietly into that good political night. His determination to clear his name of allegations of sexual impropriety has the potential to tear the Scottish Government and the SNP apart. The two most important politicians in the modern history of Scottish nationalism have been pitted against each other at the very moment the party needs to unite over the future of independence.

We've had the extraordinary spectacle of the former First Minister, and SNP leader, conducting a war of legal words over social media with the current First Minister, and SNP leader. In lengthy posts, Nicola Sturgeon defended the anti-sexual harassment procedures she introduced in January, and insisted on fairness for the complainants. Alex Salmond has condemned that due process as an unfair kangaroo court. Worse, he's accused the Scottish Government of leaking salacious details of the allegations to undermine him. Mr Salmond has even raised an action against the Scottish Government in the Court of Session.

For their part, Scottish Labour say that Nicola Sturgeon should already have suspended her predecessor from the party. That she has failed to follow the precedent set by the expulsion of the former Children’s Minister, Mark Macdonald. No formal complaint been lodged, however, with the SNP that could trigger such a disciplinary procedure. But to the dismay of many members, Ms Sturgeon has pointedly failed to rule out Mr Salmond's future defenestration. She can't.

The FM faces an acute dilemma. Under the Scottish Government’s procedures, complaints against former ministers are assessed by the civil service. If the result is problematic it is handed to the First Minister, “in their capacity as party leader”, so that the FM “can take action to secure the highest standards of behaviour in the current administration”. It's not clear what actions should be taken here, but you can be pretty sure critics will insist that suspension from the party is one of them. The allegations have been serious enough to be handed to the police.

However, the usual resignation argument that a minister cannot do their job properly until they've “cleared their name” does not apply. Alex Salmond sits in no parliament, holds no senior position in the party and is merely a sometime television presenter.

Labour's Rhoda Grant called for Mr Salmond to be suspended in order to create “a safe space” for his accusers – the two women who have made complaints. But it's not at all clear what kind of threat he is supposed to present to these women, or how removing Mr Salmond's membership card would make the space they occupy any more safe. The implication that Alex Salmond is some kind of crazed sex criminal, who cannot be allowed to walk free, is appalling. He's been found guilty of no improper conduct whatever.

Of course, the real damage was done by whoever leaked the confidential details of the allegations that he sexually assaulted two women. This vastly increased pressure on the First Minister to suspend Mr Salmond for the duration. He strenuously rejects the allegations and says he's been denied the right to see the evidence. That's assuming there is any concrete evidence.

Police and government agencies tend to work nowadays on the supposed Macpherson Principle that “victims should always be believed”, which is sometimes taken to mean that actual evidence is superfluous. Following a succession of miscarriages of justice, the Metropolitan Police has now abandoned this inversion of the presumption of innocence, and changed its guidance to say that accusers should be “listened to” rather than their allegations automatically accepted as fact. But it may be too late for Alex Salmond. In politics, you are now guilty until proven innocent. All the parties have tended to suspend politicians when allegations become public.

Many in the SNP are dismayed that Ms Sturgeon did not, at the very least, give her former mentor some kind of positive character reference last week, and then refuse to comment further. The First Minister placed herself at the forefront of the controversy, declaring that she was “100%” behind the Permanent Secretary, Leslie Evans, whom Mr Salmond's supporters believe has acted as judge and jury. Her remark that the complaints couldn't be “swept under the carpet” sounded damning.

The unalloyed glee among opposition politicians at what they see as the final humiliation of their greatest former foe is matched in the SNP by a kind of existential despair. It is hard to convey just how important Alex Salmond is to the independence movement. Political journalists and Women for Independence may regard the former leader as a hangover from alpha male politics, but for many ordinary nationalists he has hero status, comparable to that of Charles Stewart Parnell, the 19th century Irish Nationalist with whom Salmond used to compare himself. Unfortunately, that career ended with a sex scandal, too, over Parnell's adultery.

Irish nationalists always believed that Parnell was brought down by Establishment dirty tricks. There is an unshakeable conviction among many in the SNP that today's scandal must be, if not the work of M15, then a move by the deep state to silence an influential voice on the eve of a possible announcement of a second independence referendum. Salmond promised in his so-called Morningside Declaration in May to return to front line politics as soon as indyref2 is announced.

But if this is an establishment plot, then the unfortunate reality for Nationalists is that Nicola Sturgeon finds herself at the apex of it. As the new parliamentary term begins she'll come under intense pressure to suspend Mr Salmond from the party, or be accused of favouritism and hypocrisy. But if Alex Salmond were expelled on the eve of the most crucial SNP conference in years, the consequences would be unimaginable. The SNP has not just been rocked by this development it has been traumatised – and it may never be quite the same again.