The nationalist narrative, when presented as a densely packed wall of rhetoric which trials on countless doorsteps have proven to be highly persuasive, is often difficult to refute without becoming technical to the point of tedium. It’s a significant challenge facing the unionist parties.

For example, the SNP’s simple narrative about oil — that ‘successive Westminster governments’ have tried to ‘suppress the truth’ about ‘Scotland’s oil wealth’ flowing into ‘London coffers’ and being ‘wasted’ — is accepted as reality by many who are predisposed to believe it.

Specifically what perspectives and/or prejudices lead to such predilection is a vexed question best left for another time. But they are certainly widespread — hence the centrality of oil to the latest phase of the SNP’s so-called national conversation on independence.

And so I was struck by the rhetorical nature and inaccuracies of John Swinney’s quote in today’s Press & Journal. To enable a comprehensive deconstruction, I’ve tackled it in three blocks.

John Swinney: “Official figures showed that an independent Scotland would move up the EU league table from 10th to 3rd in wealth per head, with our North Sea oil and gas resources included in Scotland’s accounts.”

That’s basically a repetition of something Mr Swinney said in June 2008, except that on that occasion he qualified it by including the phrase ‘as North Sea oil revenues soar’.

You may recall that in June 2008 Brent crude was well on its way to a peak of $147 per barrel the following month. It’s half that now. Yet despite oil prices not now ‘soaring’, Swinney has repeated his claim, simply omitting its now irrelevant basis. An inconvenient truth.

Neither are these ‘official figures’. They actually arose from a May 2008 projection by Maurice Fitzpatrick of Grant Thornton, who estimated a £4.4 billion surplus for an independent Scotland, predicated on £12.2 billion in oil and gas revenues. That’s a figure which — while about right for 2008/09, in which oil prices slowly peaked to a record high and then fell away again — is by no means representative, so should not have been used to make a general point.

Indeed, there has not been a single year since records began in 1964 when even the SNP’s claimed 95% ‘Scottish share’ of UK revenues has been that high. The average annual ‘Scottish share’ for the decade 2000-10 (including projections for this year and next) is only £6.7 billion.

On the rhetorical side, note the use of ‘our’ for oil and gas. It’s a claim of rightful ownership.

Finally, ‘wealth per head’ is misleading. The report considered only raw GDP per capita, not tax rates, cost of living or other pertinent factors. Norway, for example, has much higher tax than Britain (44% of GDP against our 38%) and a cost of living about 25% higher than ours.

John Swinney: “Adjusted for inflation, some £230billion of tax revenue has come directly from Scottish territorial waters over the past 30 years. This is the reality that the London-based parties have been desperate to suppress for decades, but the truth will out.”

This is conspiratorial drivel. Nobody is ‘desperate to suppress’ tax statistics. Oil and gas revenues are published on the DTI and DECC websites. Swinney’s game here is to portray the ‘London-based parties’ as anti-Scottish. It’s ‘England expects...’ with a thin veneer of modernity.

Swinney’s reference to ‘Scottish territorial waters’ is an example of compelling but inaccurate rhetoric. He means the area of sea which, were Scotland independent, would form its territorial waters. Pointing that out may be seen at best as pedantic and at worst as denigratory. But not challenging such rhetoric allows it to become part of broader public perception. Catch 22.

John Swinney: “Norway’s oil fund, established little more than a decade ago, is now worth over £200billion, securing the benefits of their oil wealth virtually forever. If we are to enjoy the same benefits from our oil as Norway, then we must make our own future as an independent nation and learn the lessons of Westminster’s deceit.”

To suggest that Scotland could enjoy ‘the same benefits as Norway’ is grossly misleading.

Firstly, the CIA World Factbook estimates that Britain has 3.6 billion barrels of proven oil reserves. Norway has almost double that: 6.7 billion. Norwegian oil production is about 75% higher than the UK’s. Norway still has sizeable oil exports whereas Britain is now a net importer. Norwegian government revenues from oil and gas are about 2.3 times ours.

But it isn’t in Swinney’s interests to mention any of that, and so some people will have inferred that he thinks we too could accumulate a £200 billion fund within a decade.

He doesn’t actually believe that, of course. The most Swinney has ever claimed is that “SNP proposals ... could result, within 10 years, in a Scottish fund worth almost £90 billion and producing annual investment revenues of £5.5 billion.”

So let’s see: £5.5 billion annual revenue from a principal sum of £90 billion corresponds to 6.1% return on capital. At that growth rate, the accumulation of the £90 billion would require the allocation to the fund of around £6.6 billion for each of the first ten years after independence.

But we wouldn’t have that sort of money going spare. GERS 2008, for example, published under this administration, found a fiscal deficit for Scotland of £3.8 billion, including a similar geographic allocation of UK oil and gas revenues to Scotland as might occur under independence.

Diverting a further £6.6 billion would give us an annual fiscal deficit around 10% to 12% of GDP, even before factoring in our per capita share of the UK’s currently very considerable public debt.

So where is the scope for the kind of corporation tax cuts that the SNP like to tell us could stimulate rapid economic growth? That huge fiscal gap would have to be filled through some combination of additional taxes, public service cuts and/or government borrowing. It’s a circle which, however hard the nationalists might close their eyes and wish, simply couldn’t be squared.