THE SNP has been accused of "anti-austerity posturing" after a leading independent think-tank calculated that the Nationalists' plans would see a longer period of belt-tightening for Scotland compared to those of the main UK parties.

Nicola Sturgeon dismissed the Institute for Fiscal Studies (IFS) analysis as ''full of assumptions and speculations'' and stressed the think-tank had got "the SNP's plans wrong''.

The row follows an earlier one when the think-tank predicted that the so-called "black hole" in Scotland's finances, should it achieve the Nationalist goal of full fiscal autonomy, would increase from £7.6bn this year to almost £10bn by 2020.

In its latest report, the IFS criticised all the main parties, saying they had not set out "anything like full details" on plans to cut the deficit and, consequently, voters had been left "somewhere in the dark".

It noted how voters faced a "really definite choice" between £90bn of extra borrowing under Labour or £30bn spending cuts under the Tories; the biggest difference in approach, it said, since the 1992 election.

On the SNP manifesto plans, it confirmed they would increase total public spending in real terms in each year of the next parliament.

But the think-tank warned simply freezing departmental spending over the course of the next parliament would "not be quite enough to deliver" the expenditure plans set out in the Nationalists' manifesto.

This would mean, it argued, the SNP would "need to cut 'unprotected' departmental spending in real terms by 2.5 per cent (£6bn) over the four years from 2015/16 to 2019/20".

The issue was raised at First Minister's Questions at Holyrood when Ms Sturgeon insisted the IFS had simply got her party's plans wrong.

"Firstly, it doesn't credit for any increases in revenue from the tax rises we are proposing. Secondly, it gives no credit for the revenue we would increase from cracking down on tax avoidance."

She added: "The fundamental misassumption at the heart of the IFS report...is this one: it assumes the SNP would cut borrowing by 2019/20 to 1.4 per cent of GDP; that's not our plan. Our plan is for borrowing in that year to be 1.6 per cent of GDP. So those are what I would describe as the misassumptions in the IFS report."

But Kezia Dugdale for Scottish Labour, hit out at the SNP leader, telling her: "You can dismiss some of the experts some of the time, you can't dismiss all of the experts all of the time."

Later, John Swinney, the Deputy First Minister, branded the IFS analysis as flawed, saying: "SNP plans will see real-terms increases in government spending, not cuts" and added: "The only way to end austerity and to protect spending in Scotland is with a vote for the SNP and a strong team of MPs in Westminster."

But Labour's Margaret Curran, the Shadow Scottish Secretary, added: "For all the bombast and the bluster of the SNP it has now been conclusively shown that their anti-austerity posturing is nothing more than a front. Their plans would extend austerity and harm Scotland."

Scottish Conservative deputy leader Jackson Carlaw said the IFS report "exposes the lie that the SNP would somehow usher in this glorious era of wealth and prosperity" while Willie Rennie for the Scottish Lib Dems said it showed austerity would be dragged out for longer, "saddling the next generation with more debt".