ALEX Salmond and other SNP ministers were wrong when they said oil would be a “bonus” not a basis for the Scottish economy after independence, a senior party figure has conceded.

Andrew Wilson, who is leading an SNP review updating the case for independence, admitted North Sea income was “baked into” spending plans, rather than treated as a windfall.

The mantra “oil is a bonus” was a key part of the Yes campaign in 2014, and was used to rebut criticism that an independent Scotland would be overly reliant on a volatile industry.

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The phrase was used by then First Minister Mr Salmond, his then deputy Nicola Sturgeon, by then Finance Secretary John Swinney, then Energy minister Fergus Ewing and by the SNP’s then Treasury spokesman at Westminster Stewart Hosie.

The Scottish Government’s White Paper on independence predicted oil would raise up to £7.9bn, or 12 per cent of the public finances, in the first year outside the UK, 2016-17.

Crucially, oil was assumed to keep Scotland’s deficit a manageable 3.2 per cent of GDP.

However the subsequent oil price slump has cut North Sea revenue to zero, and Scotland’s deficit last year was 9.5 per cent of GDP, more than double that of the UK.

Ms Wilson, a former SNP MSP who Ms Sturgeon appointed to chair the SNP’s Growth Commission six months ago, told the BBC the “bonus, not a basis” line had been false.

He said: “We did have oil baked into the numbers and it was indeed a basis.”

His Commission had therefore assumed oil revenue would stay zero after independence and any North Sea cash would be used “as a proper windfall” to be invested in long-term projects rather than day-to-day spending, he said.

“Oil’s not a particularly helpful argument - because it gives the suggestion that somehow there’s a free lunch and that we won’t have to work, and of course we all will have to work no matter what happens. Independence would give us more tools and that’s what’s different.”

Tory Murdo Fraser said Mr Salmond's “bluster and evasion” in 2014 was finally exposed and he should admit to trying to “mislead people on oil”.

Labour’s Jackie Baillie said the SNP had offered a “rose-tinted fantasy of an independent Scotland’s finances", which had been “a figment of Alex Salmond’s imagination”.

Scottish LibDem leader Willie Rennie said: “Of course oil is not a bonus and now it hardly raises any revenues at all so we face a £15bn black hole.

“The SNP will need to explain which public services will be cut to pay for independence.”

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An SNP spokesman said: “Instead of rejoicing in the downturn affecting the North sea oil industry and the jobs affected by it, the Scottish Tories should be lobbying for support for the industry in this week’s UK Budget.

“The North Sea industry will be an important one for years to come, but the biggest threat to Scotland’s prosperity, jobs and livelihoods comes from a Tory hard Brexit, which threatens to take us off an economic cliff edge.”