ALEX Salmond's former policy chief has launched an extraordinary attack on the SNP, claiming its claims about the economy of an independent Scotland were "deluded".

Alex Bell, who spent two years working on the then-first minister's referendum strategy, claimed Nicola Sturgeon had given up making an economic case for Scotland leaving the UK.

He also suggested it was "morally dubious" of the SNP to promote an anti-austerity agenda without proposing a serious alternative.

Mr Bell made the comments in a blog for his new current affairs website, Rattle.

He claimed the SNP was shifting its emphasis from campaigning for independence to presenting itself simply as "Scotland's party".

He wrote: "This shift in the party’s purpose from independence to being ‘Scotland’s party’ is often read as a simple tactic.

"The leadership are disguising their main aim, sovereignty, until a referendum victory looks likely.

"In fact something else is at work.

"The SNP is shifting its emphasis because the leadership can find no way of achieving the core aim safely."

He added: "Cut Nicola and no doubt she still bleeds independence, but what she means by that is far less clear than before the referendum.

"The doubt arises because the campaign towards the 2014 vote, and the economic information since, has kicked the old model to death.

"The idea that you could have a Scotland with high public spending, low taxes, a stable economy and reasonable government debt was wishful a year ago – now it is deluded."

Mr Bell said the economic health of a newly independent Scotland, in the short to medium term, was the "only thing that mattered".

He said weaknesses in the SNP's economic plans were "obscured by lots of noise, and the SNP is accomplished at shouting".

He wrote: "The party’s success has been built on hard work and spin.

"Behind the scenes she isn’t gullible. It may work in public to rubbish claims by the Institute of Fiscal Studies that there is a gap between what Scots pay into government and what they get out in services, but only fools believe their own propaganda.

"The fact is a gap exists – Scotland does not earn enough to pay for its current level of spending. Once you accept that, you acknowledge that the SNP’s model is broken."

In a related attack, he claimed the SNP's anti-austerity rhetoric was not matched by its policies.

"SNP fine print makes it crystal clear that it will not reverse the dastardly Tory cuts on independence.

"It will not reverse the privatisations or the anti-union legislation of Thatcher and nor will it repair the cuts of Cameron and Osborne," he wrote.

"This is a morally dubious form of government. Posing as the defender of the poor against Tories when you have no credible alternative and don’t bother to research one is arguably immoral.

He said the SNP was putting "no effort" into refining its case for independence in the light of falling oil prices and confusion last year over possible currency arrangements.

The party remained popular, he argued, "for want of an alternative".

Mr Bell resigned from Mr Salmond's office in July 2013.

Exactly a year before the referendum, in September 2014, he publicly criticised his former boss's strategy, attacking the Scottish independence campaign for relying too heavily on "tedious" ideas and "tired policies".

The SNP's opponents seized on the comments.

Scottish Labour's public services and spokeswoman Jackie Baillie said:

"Alex Bell is absolutely right to say that it is wrong for the SNP to claim they oppose Tory cuts but offer no alternative. "We can see it again with tax credits.

"Scottish Labour is on the side of working families. It's time for the SNP to decide if they are too."

Scottish Conservative deputy leader Jackson Carlaw said:

"Many of the things that have come to pass – a falling oil price, the need for tough economic decisions – were warned about long before the referendum.

"We were ridiculed for making them at the time, but now even former SNP advisers are accepting these were justified.

"This is more confirmation that the SNP is merely a propaganda machine which hopes it can trick people into thinking it is a competent government."

Scottish Liberal Democrat leader Willie Rennie said: "Immoral fools with no credible alternative is a powerful condemnation from someone who knows the SNP leadership well."

An SNP spokesman said:“In the year since the referendum every opinion poll conducted on the matter has shown an increase in support for independence, with some putting Yes ahead.

“This is due to the widespread anger that the UK Government has not delivered on their Vow on more powers for Scotland – but also because the SNP continues to make the case for self-government for Scotland, and demonstrate a strong track record in office.”