THE SNP’s blueprint for independence would extend Tory austerity, and fails to factor in the rising cost of health and social care, one of its contributors has warned.

Economist John McLaren also said the party's Growth Commission failed to deal properly with the start-up costs of an independent state and its inherited debt.

However he said the implied austerity could be avoided by targeted spending cuts and and tax hikes, such as a new whisky tax, at the point of independence.

The SNP issued the 354-page Commission report in May to help refresh its economic case for independence.

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It proposed a decade of tight public spending after a Yes vote to halve Scotland’s deficit, keeping the pound, and saving all North Sea oil revenue.

Nationalist critics said it was not radical enough, while the Institute for Fiscal Studies said it would continue austerity, something the SNP dispute.

In a briefing paper for Scottish Trends, Mr McLaren, who contributed early background work to the Commission, said it had many strengths, including support for migration, dropping a formal currency union with sterling, and more realism about oil.

However it also lacked transparency on future spending restraints, debt levels, the Brexit-like costs of leaving the UK single market, and start-up costs.

He highlighted a failure to account for higher inflation rates for health, social care and welfare, and said protecting these areas implied a 15 per cent cut in the other half of the budget over a decade.

He said that instead of focusing on spending restraint, a newly independent Scotland would be better hiking tax and making some cuts on day one to avoid austerity.

He said cuts to defence and economic development, shorter university courses, and uprating benefits by the lower CPI rate of inflation could help save £3bn a year.

A rise in income tax, closing VAT loopholes, new taxes on tourism, wealth, land and whisky, and charging for some health services, could also raise £3bn a year.

The net impact would be Scotland starting with a deficit of around 4 per cent, rather than the 7.1 per cent envisaged by the Commission, avoiding the need for a decade of austerity.

Mr McLaren said that at the start of independence, risks would dominate opportunities, although these may balance out over time, adding: “Any notion that Scotland’s economic performance will automatically, or even probably, improve as a result of independence is a hope rather than an expectation based on hard evidence.”

He added: “While [the report] has strengthened the arguments in some areas, in others doubts remain. In particular, it is difficult to see how another decade of austerity, involving real terms cuts in around the half budget, can be achieved.

“As a result, upfront savings need to be made rather than relying on an extended period of change which simply delays and prolongs the necessary fiscal adjustment.”

Scottish Labour leader Richard Leonard said: “This report confirms yet again that the SNP’s plans for an independent Scotland would result in austerity cuts that not even George Osborne would have dared to impose. The weight of independent, academic evidence demolishing the SNP’s cuts commission is growing greater by the day.”

Scottish LibDem leader Willie Rennie added: “This new analysis confirms that an independent Scotland would have no choice but to impose austerity on public services.

"Even Nicola Sturgeon's own commission of friendly experts can see no other way forward.

"To protect the NHS, an independent Scotland would have to machete every other service.”

SNP deputy leader Keith Brown, who is overseeing a consultation with SNP members on the Commission, said: “The Sustainable Growth Commission’s report has given us all hope for an alternative to the Tory chaos over Brexit. The SNP approach will be to continue to reject austerity, and our focus will be to grow the economy and invest in Scotland’s future.”