AN independent Scotland would remain home to the UK's nuclear deterrent for a generation because there would be nowhere else to put it, a former SNP adviser has warned.

Stuart Crawford said the lack of an alternative site meant the Trident submarines based at Faslane and the warheads stored at nearby Coulport would take 20 to 25 years to remove.

He said the government of an independent Scotland should therefore charge the Ministry of Defence around £1bn a year to keep the weapons north of the border.

The timetable, which is four times the one in the SNP’s 2014 independence plans, is likely to anger party activists committed to the rapid removal of Trident.

With Nicola Sturgeon considering whether to press for a second independence referendum in light of Brexit, the SNP is currently updating its prospectus for life outside the UK.

However to date the party’s efforts have focused on the economic case for independence.

Mr Crawford told Scotland on Sunday an independent Scotland could not sensibly demand Trident's removal from the Clyde for many years after independence.

Although there are other potential homes for the submarine fleet, including Devonport and Barrow-in-Furness, nowhere else in the UK has the equivalent of Faslane’s sister site at Coulport, where missile warheads are stored.

The issue is not new - indeed, many in the SNP see the lack of an alternative base as a way for independence to force the UK to abandon its nuclear deterrent.

However Mr Crawford, a former army officer who previously advised the SNP on defence and is publishing a paper on the subject in the autumn, said the party hard to be practical about Trident.

He said: “An independent Scotland cannot really sensibly insist on removal of the UK’s nuclear deterrent from its waters in the short to medium term.

“Therefore some pragmatic solution has to be adopted. The pragmatic solution is, in my opinion, to rent the Faslane nuclear facilities to the rest of the UK until such time as some other arrangement can be brought about.

“If there is any chance of Scotland becoming an independent country in 2021, it would take the UK government at least 20 years to build the equivalent to the Faslane/Coulport facilities elsewhere in the UK." The White Paper on independence published by then First Minister Alex Salmond said Trident could be gone within five years.

It said: “Following a vote for independence, we would make early agreement on the speediest safe removal of nuclear weapons a priority. This would be with a view to the removal of Trident within the first term of the Scottish Parliament following independence.”

Mr Crawford said: “It is the most emotive defence-related issue in the whole independence debate.

"The difficult thing for the SNP leadership would be selling this to the foot soldiers. The broad base of the independence movement is very much grounded in the CND movement. I am completely sympathetic to that.

“The SNP Government might look at this plan and say it doesn’t deliver our promise to remove Trident, but it would be the biggest bargaining chip that an independent Scotland could have.”

Tory MSP Douglas Ross said: “These comments add an element of realism to the SNP’s defence policy for an independent Scotland. However, the idea of the UK’s nuclear deterrent remaining on the Clyde for 20 years would not sit well with many rank and file nationalists. “It was never credible to think that Trident would just disappear from the Clyde following a Yes vote. There are thousands of Scottish jobs that depend on it. This is another example of policy and decision-making being driven by political dogma and the SNP’s obsession for separation at any cost.”

An SNP spokesperson said: “The SNP does not support Trident either as part of the UK or in an independent Scotland. We have continually opposed the renewal of Trident at the cost of conventional and cyber defences and continue to do so.

“In 2014 the Scottish Government set out a responsible approach to the removal of Trident from Scotland and in the event of independence securing the speediest and safest withdrawal of nuclear weapons would be a priority for an SNP Scottish Government.”