At the beginning of 2014, just as the independence referendum campaign was stepping up a gear, Alex Salmond, made what seemed to be a startling admission.

Independence, he said, would not solve all Scotland's problems.

Interviewed by broadcaster James Naughtie during an event co-sponsored by The Herald, the then First Minister told his audience that leaving the UK would not lead to homes being fitted with "three taps, for oil, whisky and water".

"I suspect we'll never have no problems, but I'm certain we can do better than we are doing now," he mused.

On one level, it was a throwaway line in a wide-ranging and convivial conversation. But it was also notable for being the most downbeat assessment of independence Mr Salmond was to make for the remainder of the campaign.

By that stage, the SNP's independence blueprint, its White Paper Scotland's Future, was already making grand predictions about the country's oil revenues and promising an instant bonanza of tax cuts, improved pensions, generous childcare and other giveaways costed at £1.2 billion.

Most Scots were rightly sceptical. Since its referendum defeat in September 2014, the SNP has been edging towards a more sober view.

Largely, that has been forced upon the party by the collapse in oil revenues and the growing gap between Scotland's and the UK's public finances.

The last set of figures showed Scotland running a deficit of £14.9bn, proportionately twice that of the UK as a whole. Wiser heads in the SNP called for a more honest approach to the economics of independence and earlier this year First Minister Nicola Sturgeon promised to be "realistic and relevant".

That is the background to a new vision of independence outlined by the SNP MP George Kerevan. Leaving the UK, he admitted, would require a period of austerity. Not only that, state assets inherited from the UK would have to be sold off to raise revenues to prop up a new Scottish currency.

Mr Kerevan argues that would be a price worth paying to gain powers that would transform Scotland into an economic powerhouse.

Labour and the Conservatives have been scathing about his comments which, it should be noted, do not reflect an official SNP position. Not yet, at least. The party would be unwise to disown a narrative that is potentially more persuasive than the "land of milk and honey" vision of two years ago.

The question as we contemplate the prospect of a second independence referendum is this: How realistic is the rebooted case for leaving the UK?

Mr Kerevan says the economic pain would last five years, a figure that seems to be plucked from thin air. He also writes boldly of soaraway economic growth without explaining how that might be achieved.

News today showing the Scottish economy failing to grow, lagging the UK and with little apparent hope of an upturn anytime soon, shows the scale of the task.

Coming up with a new independence story that smacks of realism does not necessarily make it any more realistic. If we are to have a second referendum, both sides have a duty to debate the vital economic issues seriously and honestly.

But for now, simply by accepting that independence would not be an instant panacea, the SNP appears to moving in the right direction.