PARTY conferences are bubbles. Or rather, bubbles within bubbles. A small pocket of members of a club which is itself a fraction of society at large. But like all bubbles, they’re still liable to go pop.

The SNP conference in Aberdeen this weekend isn’t especially susceptible to this phenomenon. But some in the leadership seem to have forgotten it still applies to them. The cause of the cocky attitude, ironically, is what has been promoted as a healthy injection of realism.

It’s not the fault of the Sustainable Growth Commission chaired by former MSP and current corporate lobbyist Andrew Wilson. Its 354-page report was intended to sketch out a blueprint for independence and stimulate discussion, and it has achieved both.

The problem is that, having taken 20 months to arrive, it has assumed a semi-mythic status. It is unhelpful to be seen as the answer to many prayers. But it comes with no guarantee of salvation, and those who regard it as the game changer the independence movement has been waiting for should take a deep breath. It offers as many problems as solutions.

Nevertheless, Nicola Sturgeon and her ministers have welcomed it enthusiastically. The general impression they give is that the report is a turning point for the cause. Not a new beginning, as much is familiar, but certainly a more appealing modernisation.

It is has infuriated many on the left of the Yes movement, but Ms Sturgeon is coping well with their agony, reasonably assuming they will vote Yes again when it comes to the crunch. The report is there to reassure and cajole the 55 per cent, not thank the 45 per cent. Indeed, one of the first things Keith Brown said when he was elected the new SNP depute leader yesterday was that he wanted to debate the report beyond the party walls, reaching out to business groups and civic Scotland. The SNP’s boardroom charm offensive, run in the old days of devolution by John Swinney and Jim Mather, is evidently undergoing a revival.

But I suspect the SNP leadership is falling prey to its own hype. It has assumed the report will be readily accepted in the party – Ms Sturgeon has predicted a “very positive” reception – and, equally prematurely, assumed it will go down pretty well in the country at large.

Even in the inner bubble of conference, there were some clues that’s not so. One of the busiest fringe events on the first day in Aberdeen was a meeting to discuss the economics of independence. There were some interesting contributions from MSP Joan McAlpine and MP Kirsty Blackman. Ms McAlpine reflected that the party’s past advocacy of corporation tax cuts needed more subtly, while Ms Blackman talked about aping the Do it for Denmark campaign to grow the population, coyly suggesting "Shag for Scotland".

But the panel member getting the loudest applause was the one with the toughest criticisms of the Growth Commission. Former MP George Kerevan said the “conservative” plan to keep the pound would leave a newly independent Scotland “at the mercy of the banks”, while tight public spending to cut the deficit risked independence offering nothing for the poor. The audience looked a fairly typical slice of the SNP. There was a lot of grey hair and earnestness. Yet a great many appeared to share Mr Kerevan’s concerns.

But the starkest reminder that turning out a report is not the same as turning a corner came when Ms Sturgeon was interviewed by Channel 4 News. It was not her finest hour. Despite being at the apex of the Yes movement, she was unable to say how much it would cost to set up an independent state. This is no small detail. After trying to dance around the question, she finally admitted she couldn’t remember the figure in the Growth Commission report.

It resurrected all those memories of the 2014 referendum, when the Yes side was peppered with questions about the bill for leaving the UK. The Commission’s number – a bargain £450m over five years – also echoed the naive optimism of many of the figures put around four years ago. As the Channel 4 journalist pointed out, it’s costing Scots taxpayers £200m to set up a part-devolved social security system. So £450m for a new country?

Amid a choking raft of poor statistics in education and health, and with the grassroots Yes movement agitating for a swift referendum, it is understandable that the SNP leadership is trying to shift the focus on to independence through the Growth Commission.

But, as Ms Sturgeon’s interview showed, it is dangerous to use the report as a campaign tool without the discipline of a campaign to back it up. Talking about independence as if her autumn decision on a referendum is already made simply invites questions of the kind that kept the Yes campaign on the back foot in 2014. The SNP is running ahead of itself. The Growth Commission is only one bubble in the national tide required to secure its goal.