Image copyright Ministry of Defence Image caption Nuclear weapons would be removed from an independent Scotland by 2020 under the Scottish government's proposed timetable

Moving Trident nuclear submarines out of an independent Scotland would be very difficult but "not impossible", according to a study.

The report by the Royal United Services Institute (Rusi) also said relocating the submarines would be far cheaper than previously assumed.

But it could take a decade to build a base for the submarines elsewhere in the UK, it said.

The SNP wants to remove nuclear weapons within four years of independence.

The submarines carrying the UK's nuclear deterrent currently operate from the Faslane naval base on the Clyde.

There have been concerns over how they could be relocated in the event of a "Yes" vote in September's independence referendum.

Milford Haven in Wales and "the most obvious replacement", Devonport base in Plymouth, have been suggested as potential new homes for the submarines.

Falmouth in Cornwall is named as a possible munitions site.

The UK government has choices on what it decides to do with its nuclear weapons following their removal from an independent Scotland Scottish government

Former cabinet minister Lord Forsyth has previously warned that the potential difficulties of moving the submarines would mean that the UK could be forced to give up its nuclear deterrent if Scotland votes in favour of independence.

But in their paper, Rusi research analyst Hugh Chalmers and research director Malcolm Chalmers said relocating Trident would be both financially and technically feasible.

They suggested that recreating the required nuclear facilities outside Scotland would add between £2.5-3.5bn to the cost of maintaining a nuclear-armed fleet, plus the cost of acquiring and clearing land.

This would be far less than a previously-predicted £20-25bn, they said.

Hugh Chalmers said the research by the military think tank contrasted with an "unlikely consensus" between supporters and opponents of Scottish independence that it would be impossible to relocate the nuclear weapons elsewhere.

If the question mark over Trident's future could be answered, it would help untangle a difficult issue surrounding Scottish independence, he added.

Analysis: Jonathan Beale, BBC defence correspondent

Britain's nuclear deterrent doesn't come cheap. It'll cost around £20bn to replace the current fleet of four Trident submarines, sometime during the next decade.

Not everyone's convinced - either in Parliament or the MOD - that the UK can afford or really needs a like for like replacement.

This study, by the distinguished defence think tank Rusi, highlights the additional costs if Scotland votes for independence.

It concludes that moving the deterrent from the Clyde and the secure storage facilities for the warheads at Coulport is financially and technically feasible but wouldn't be cheap - between an additional £2.5bn to £3.5bn.

It'll also cost a lot of political capital - persuading people of Plymouth and Falmouth that it's in their interests to have the deterrent and warheads based in their backyard instead.

The Ministry of Defence has already had to cut its cloth to the tougher economic climate. It would rather not contemplate an even bigger dent to its finances as a result of a "Yes" vote.

Mr Chalmers said: "When people start considering options for relocations it's only natural to assume that it would be quite expensive and very difficult and that is certainly the case. But importantly it is not impossible.

"We estimate that essentially the net costs of relocating could actually be £2.5-3.5bn at 2012 prices, rather than the tens of billions or even £20bn that has been put forward so far."

It is difficult to estimate the total costs, or how long it would take, to replicate the facilities at Faslane, but it would likely cost taxpayers billions of pounds and take many years Ministry of Defence

But he said it would take a long time, and was unlikely to be completed by the SNP's target date of 2020.

Mr Chalmers said: "It may be possible to deactivate Trident by that point and have it out of Scotland but it's unlikely we would have been able to have it up and running in a new location by that point.

"The Scottish government has acknowledged that if they were to become independent there would be a period of time where the UK would be basing its nuclear forces in an independent country. The UK would be the first country to ever do this."

A more "natural timeframe" would be linked to the entry of a new generation of nuclear-armed submarines, currently anticipated to start in 2028, he argued.

Mr Chalmers said the Rusi paper showed the possibility of a "space for a friendly and amicable settlement" over Trident in the event of independence.

He added: "Effectively this is a key aspect of any negotiations that will emerge after a Yes vote.

"This will be a very, very important issue. If both Scotland and the UK can show that they can come to some sort of amicable arrangement then that untangles a very knotty issue.

"We are trying to essentially dispel the myth that relocating Trident out of Scotland is impossible and in doing so create some space allowing an amicable settlement to be reached in the event of a Yes vote."

'Speedy withdrawal'

A spokeswoman for the Scottish government said: "As Rusi's paper shows, the UK government has choices on what it decides to do with its nuclear weapons following their removal from an independent Scotland, including of course the potential to reconsider the possession and planned renewal of Trident.

"The Scottish government will work responsibly with the government in Westminster in securing the speediest safe withdrawal of Trident from an independent Scotland.

"We look forward to the opportunity to discuss these arrangements with the UK government following a vote for independence."

A Ministry of Defence spokeswoman said: "There are no plans to move Trident from Her Majesty's Naval Base Clyde and unilateral disarmament is not an option.

"We are not planning for Scottish independence and as such it is difficult to estimate the total costs, or how long it would take, to replicate the facilities at Faslane, but it would likely cost taxpayers billions of pounds and take many years."