There used to be a reassuring amateurism about the SNP conference: tombolas and pamphlet stalls; no security to speak of; anyone allowed to speak their mind; more a gathering of like-minded eccentrics, like a car owners club.

Now the SNP has grown into a serious governing party and its annual conference has evolved accordingly. There will be nearly 5,000 in Aberdeen, including about 1,500 from the media, business and PR.

The place will be crawling with commercial lobbyists promoting airport runways and oil and gas interests. Jim Ratcliffe's Ineos has reportedly paid £4,000 for a fracking stall. Former party workers will be making introductions and definitely not trading on their contacts.

I'll even be there flogging advance copies of my new book Tsunami (we're all trying shamelessly for a piece of the action). I was supposed to be speaking at a fringe event organised by the Law Society of Scotland but it has pulled out following claims of partiality in its investigation of the property lawyer of Michelle Thomson MP, who withdrew the SNP whip.

It's a cheap shot to say the SNP conference has become like all the others: a centrally-controlled media event with a vaguely sleazy fringe. But it is acquiring establishment habits, such as fear of controversy. The conference agenda has been swept for divisive issues that might disturb the image of a united party on its way to a third successive victory at the Holyrood elections in May.

The fracking decision has been shelved and the moratorium extended to unconventional gas. When should the SNP hold the next independence referendum? When Nicola says. An independent currency? Ditto. Concern about watering down the Land Reform Bill will only surface on the conference fringe.

There's nothing particularly sinister about this. All successful parties try to present a united front and avoid the kind of internecine warfare into which Labour has descended. Actually, the SNP's almost scary party unity is genuine and arises from its members' trust and belief in Nicola Sturgeon.

Nothing succeeds like success and the SNP won the biggest election landslide in history in the May general election. Why wouldn't it honour the leader's achievement? Labour has been obliterated in Scotland, losing 40 of its 41 seats. The SNP has established itself as the dominant force in Scottish politics for the foreseeable future. The First Minister has won the affections of Scottish voters in the way her predecessor, Alex Salmond could not.

If they are sensible, party managers will allow some controversy to develop if only to avoid the charge of being control freaks. The tens of thousands of new members will rapidly lose faith in the SNP as a vehicle for radical political change if they find they’ve just joined a Caledonian version of New Labour.

You sometimes think the SNP needs to be saved from itself. It certainly needs to be saved from the vociferous Nationalist partisans on social media who regard any criticism of the Scottish Government as biblical heresy. The problem is that many members seem to believe that the independence movement belongs to the SNP, and that Yes supporters should automatically support the party leadership.

There's been a lively debate recently in the wider independence movement about the SNP's privatisation policies. The independence supporting video blogger, Stephen Paton, has pointed out that the SNP hasn’t exactly been bending over backwards to keep water services out of private hands. But even to mention his his name is to invite a storm of criticism from the guardians of Nationalist rectitude

They haven't got over the Michelle Thomson affair, either. Indeed, the scandal about the former SNP MP's property speculation has in part been kept alive the twitter storm of Nationalists condemning the “mainsteam media witch hunt” against this blameless individual who, after all, was only doing her bit to help poor home owners sell their properties.

And why shouldn't she make a bit of money out of it? How dare they attack this poor woman when she hasn't been charged with anything? Some SNP supporters believe it is offensive to question the business activities of SNP MPs, a defence they would never apply to all those Labour or Tory MPs in the 2010 expenses scandal, the great majority of whom were not charged with anything.

Too many Nationalists forget how they jeered and cheered when rival party leaders such as Labour's Henry McLeish and Wendy Alexander and the Tories' David McLetchie were driven from office after press revelations about their conduct. Scotland has a rigorous culture of political scrutiny; perhaps too rigorous. In none of these cases was any actual wrongdoing established.

This defensiveness is not unique to the SNP, but the paranoia is debilitating and counter-productive. Rigorous press scrutiny is the disinfectant which prevents political parties getting infected by sleaze.

They should take a lead from Ms Sturgeon, one of the very few political leaders in the world who actually manage their own Twitter account. She has been conspicuous only by her silence over the activities of her former Westminster business spokeswoman. There has been no knee-jerk defence of one of her most prominent women MPs.

Indeed the First Minister's handling of the Thomson affair has been firm, ruthless even, and exemplary. It’s not her job to clear her MPs’ names. Ms Sturgeon has prevented the SNP’s first potential sleaze scandal becoming a serious political issue at this conference; if only the "Twitternats" would shut up about it.

The First Minister will spend much of her speech this week defending the SNP's record on social justice, which has also been under attack recently from erstwhile supporters on the independence referendum front. Why has inequality continued to rise in Scotland? What about the educational attainment gap between rich and poor?

Why is unemployment higher than in the rest of the UK? The SNP has lambasted Labour for backing George Osborne's Fiscal Charter but hasn’t Finance Secretary John Swinney congratulated himself on delivering balanced budgets?

Ms Sturgeon will give a good account of herself as always. There will no doubt be newsworthy initiatives on housing, health and a withering assault on the UK Government’s Scotland Bill for failing to give Holyrood adequate powers over welfare. The First Minister is a genuine social democrat who is affronted by issues such as the failure of our universities to attract working class students and she won't duck the issue.

But the SNP's dominance of Scottish politics demands that it should be held to account in the most rigorous manner. Scotland is not a “one-party state”; that is nonsense. But the opposition parties have never been weaker here. The SNP dominates Holyrood and the First Minister has said she will be campaign to secure another overall majority in the Scottish Parliament.

It is not so long since she was saying she thought minority government was the best form of government for Holyrood. As the SNP moves into its own imperial phase, it needs critical friends more than ever. It has no shortage of critical enemies.