THE SNP has hit back at a report that says an independent Scotland could pay for its defence by leasing Faslane back to the UK, warning that Scotland should not try to “secure independence on the cheap”.

Stewart McDonald, the party’s defence spokesman at Westminster, responded to the document titled “Could an independent Scotland defend itself Scot-free?”, which suggested Trident should remain at Faslane until an alternative base is built outside Scotland.

The independently-produced paper by defence analyst Stuart Crawford and economist Richard Marsh suggests that an independent Scotland could charge £200 million per year to retain Trident and that four submarines which carry the missiles would have to stay in Scottish waters for “perhaps up to” 20 years.

The report also recommended leasing the Lossiemouth airbase to the RAF and Nato.

That clashes with the SNP grassroots which is opposed to nuclear weapons. SNP members who are CND activists called last month for the party to set a timetable of three to four years for Trident to be removed following a Yes vote.

The Scottish Government’s Growth Commission proposed a defence budget of 1.6% of GDP, about the Nato average and approximately double that suggested by Crawford and Marsh.

McDonald said: “Most Scots would find it unacceptable to have achieved their independence only to try and secure that independence on the cheap, and I have to say I agree – bringing our defence spending in line with the Nato European average would allow a comprehensive and bespoke posture for an independent Scotland.”

"As we await the publication of the UK’s Integrated Defence and Foreign Policy Review this autumn, which is likely to overlook Scotland’s unique security interests again, I don’t think anyone would necessarily want to replicate that low level of strategic ambition within that UK."

But Crawford, who once advised the SNP on military matters, has defended the report, saying that McDonald’s viewpoint “isn’t practical”.

“The SNP grassroots that are opposed to nuclear weapons think it’s a gross betrayal of everything they stand for,” he told The National.

“We have to be careful not to confuse purpose with process The purpose is to get rid of nuclear weapons on the Clyde. The process is by doing it we must make it easier for other actors in the saga to do their role. I think that’s the most pragmatic way to go about it. The SNP CND group is dead against that.

He went on: “I sympathise with that view but it isn’t practical as Trident has nowhere else to go. People say the French or Americans would take it but Faslane has a deep anchorage and nowhere else in the UK could replicate it.”

READ MORE: Stewart McDonald unveils big plans for Scotland's Navy under independence

The report’s authors also proposed a smaller conventional Scottish Defence Force than they previously outlined in their 2012 paper, “A’ the Blue Bonnets: Defending an Independent Scotland”.

They argue for a force with as few as 13,000 personnel and an annual running cost as low as £1.5 billion.

Crawford said this will not affect the international standing of an independent Scotland.

He added: “I can’t see the US being hugely unimpressed by that. There is an international movement to divest the world of nuclear weapons which I support. I don’t think it will affect how the international community’s view of an independent Scotland.”

Crawford also said reports like this are important to win votes for independence.

"People have to be presented with a broad judgement of opinion to allow them to make their own minds up," he added.

Before the 2014 independence referendum it was suggested that moving Trident could cost £20bn and take 20 years. There has long been an assumption that the UK would continue to use the base for a transition period, but there is controversy within the Yes movement about how long that would or could be.

First Minister Nicola Sturgeon is a long-standing critic of nuclear weapons and ahead of the General Election in December last year made the commitment to scrap Trident as one of her red lines for the SNP supporting Labour in the event of a hung parliament.