ALEX Salmond and his MSPs are to receive an unprecedented briefing on how an independent Scotland could thrive as a big-state, high-tax progressive country on the Nordic model, amid growing support for the idea throughout the SNP.

The so-called Common Weal plan, which has been injected into the referendum debate by the left-wing Jimmy Reid Foundation, will be the first item on the agenda at the annual away day of the SNP's parliamentary group next month.

The Foundation's director, Robin McAlpine, has been invited to address the SNP's 65 MSPs, including the First Minister, on the concept, and field questions on its policy implications.

He is expected to reassure them that the Common Weal is a hard-nosed and practical alternative to the status quo, and argue that the party should embrace it ahead of the referendum.

It is understood to be the first time that a think tank has addressed the SNP group.

The invite confirms growing interest in the idea among the SNP hierarchy, with Salmond said to be "very relaxed" about it after initial scepticism.

A senior SNP source said: "It's a good debate to have. It sets out the potential and opportunity of independence and helps with the message that people who believe in progressive politics would be better served by a Yes vote than a No vote."

The Common Weal model envisages a fundamental break with the UK's market-led economic and social model, with Scotland importing policies from Germany and Scandinavia designed to make the country wealthier, fairer and more equal.

A key part would be an expanded welfare state providing "from-the-cradle-to-the-grave" services which are paid for through an overall higher tax take.

But the Common Weal model would also entail a diverse, high-skill, high-pay economy in which Scots firms are supported by lending from state banks and favoured in state procurement.

Since its launch by a group of around 30 academics and economists two months ago, Common Weal has rapidly gained momentum within the Yes campaign -– in large part because of a lack of a competing vision from the SNP.

Yes Scotland chair Dennis Canavan has given it his support, and the Church of Scotland has set up a working group to examine its principles.

Bill Kidd, the SNP chief whip, has also called for a main hall debate on the subject at the SNP annual conference in Perth in October, and last month former business minister Jim Mather emerged as a surprise convert to the cause.

On the right of the party, the self-made millionaire Mather was instrumental in making the SNP credible with the Scottish business community ahead of the 2007 Holyrood election.

The last such event for SNP MSPs before the 2014 referendum, this year's away day will actually run over two days at Murrayfield Stadium in Edinburgh, when the group will also discuss legislation and policy ideas.

SNP group convener Gil Paterson said: "I can confirm that Common Weal is going to be discussed and there will be a question-and-answer session. The reason I've decided to put it on the agenda is that many of the group are interested in it and they want to participate."

McAlpine added: "We're delighted to have been invited to talk about the Common

Weal and I look forward to answering the many questions people will have.

"I hope we can persuade politicians of all parties that this really is the way forward for Scotland. I'm confident it reflects what a majority of Scots want for their future and that it can bring people together after years of cynicism and division."

The Reid Foundation is also taking part in the Scottish Green Party conference later this year, and has put out feelers to Labour.

Its website is compiling a library of potential policies, with six papers on key areas due out in the autumn, starting with the critical issue of tax.

Tory MSP Murdo Fraser said: "It's an indication of the trouble the Yes campaign is in that they're having to find a new narrative for what independence means and embracing this.

"It would be very bad news for middle earners and the business community in Scotland to be subject to Scandinavian levels of taxation."