A LEADING economist has accused the SNP government of undermining public trust by disguising its own inaction and exaggerating its spending with a “duplicitous” Budget.

John McLaren said that, despite ministers complaining about Westminster austerity, they had done next to nothing to boost the Budget for 2017-18 by using their new tax powers.

He said next year's £800m cash increase resulted almost entirely from decisions made by the UK government.

Read more: Alex Salmond - Yes will win next referendum if Westminster rejects Scottish Brexit deal

Just over £650m came from ‘Barnett consequentials’, the knock-on effects of spending decisions south of the border, raising the block grant to Scotland, while £135m was an increase in capital borrowing.

He said the new tax-raising powers, including those over income tax, had “turned out to be something of a damp squib, making little, if any, difference to the Budget as a whole”.

Even the SNP manifesto pledge to invest £500m above inflation in the NHS over the parliament was built on the back of a five-year spending plan for the English NHS, he said.

In a new paper for the Scottish Trends website, he said: “It seems likely that all the funds to meet this pledge will arise from NHS England-related Barnett consequentials, with no additional money from Scottish budgets or from increased taxes.”

Alex Bell, a former special adviser to First Minister Alex Salmond, said the SNP were “cowards” for failing to take bold measures on tax and we was in "despair" about the party's timidity in office.

Predicting the Budget would “slash spending”, he wrote in a newspaper column: “The poor will suffer, services will be cut, jobs will be lost all because the Nats actively chose not to build a new land, but to make do and mend. If that is the best they can offer, why bother giving them more powers?”

Mr McLaren, honorary Professor of Economics at Glasgow University’s Adam Smith Business School, also said it was “impossible” to justify Finance Secretary Derek Mackay’s claim last week that councils would get an extra £240m, based on the official Budget documents.

Scottish Parliament analysts this weekend said council funding would fall by £327m, backing up a complaint from the council umbrella group Cosla.

Mr McLaren said new capital borrowing powers were also not being used as intended, but to prop up the SNP replacement for PPP/PFI, known as NPD, which has fallen foul of EU rules.

Read more: Alex Salmond - Yes will win next referendum if Westminster rejects Scottish Brexit deal

Overall, presentational tricks were making the Budget “increasing difficult” to follow.

He said: “Such behaviour is duplicitous and undermines trust. Just because UK Budgets are often presented in a way that contains sleight of hand and manipulation doesn't mean that the Scottish Government should borrow from such ‘worst practice’.

"As the UK Government has often found out, short term tricks are usually found out and simply lead to an erosion of confidence in the Budget process. It would be far better to make clear your position and to argue the case for that position, rather than to present a false one.

“While it is understandable that politicians will want to put forward their own best interpretation with respect to difficult budget choices, we now appear to have reached a point where too often what is presented cannot be taken at face value.

"This encourages political cynicism and disengagement, the reverse of what is needed.”

Tory finance spokesman Murdo Fraser said: “After complaining for years about the United Kingdom, this analysis blows a hole in the SNP's grievance agenda.

“None of this extra cash is due to the SNP's own decisions, it is all due to the Union dividend.”

Labour’s Jackie Baillie said: “Nicola Sturgeon has campaigned her entire adult life to have the powers to do things differently to the Tories, yet now she has the powers she refuses to use them. Labour will not vote for a budget that cuts public services even further.”

It also emerged yesterday that public support to nationalised Prestwick Airport will hit £40m next year, despite ministers predicting a £25m limit when they bought it for £1 in 2013.

Read more: Alex Salmond - Yes will win next referendum if Westminster rejects Scottish Brexit deal

A government spokeswoman said the Budget would deliver increased investment in education and the NHS, and provide support for the economy, jobs and household incomes through a "fair and balanced set of tax and spending proposals".