Devonport is obvious alternative to Faslane for Britain's nuclear missiles, says Rusi thinktank, despite risk of 'accidental ignition'

There would be no insurmountable technical or financial obstacle to relocating Britain's Trident nuclear missile base to England out of an independent Scotland, a report by a leading thinktank says on Thursday.

Any local opposition might delay but not stop relocation, and the favoured site would be Devonport in Plymouth, it says.

Some opponents of Scottish independence have suggested it would mean the end of the Trident nuclear weapons system and that the cost of moving the submarine base at Faslane and the nuclear warhead depot at Coulport would be prohibitive.

The study by the Royal United Services Institute (Rusi) says that relocating Trident would add up to £3.5bn to the cost of retaining the UK's nuclear forces. The cost of the overall nuclear deterrent programme over 25 years is estimated to be £80bn.

It says that while any relocation could not be completed by the 2020 target date currently proposed by the Scottish government, it could be put off until 2028, the date the new fleet of Trident submarines is due to start entering service.

Devonport, the base for conventionally-armed nuclear submarines, would be the most obvious alternative to Faslane, says the report.

The option "given most credence to date" for storing the submarines' nuclear warheads is the Fal estuary to the north of Falmouth which offered "good shelter and a comparatively isolated location", the report notes.

Milford Haven, cited in the 1960s as a possible Trident base, would be ruled out as 25% of the UK's liquefied natural gas passes through its terminals.

The study acknowledges there would be safety concerns: "Introducing nuclear-armed [submarines] to Devonport will unavoidably introduce a new risk that an accidental ignition of one or all of a submarine's Trident D5 missiles could spread radioactive material over some of Plymouth's 260,000 inhabitants."

Though there would be opposition on safety grounds, it notes that the Ministry of Defence is reported to have waived safety requirements at Coulport in the 1970s to allow that base to continue operating.

It notes: "The secretary of state has the power to restrict the examination of plans to only those with suitable clearance in a case that 'may involve the interests of national security'. Furthermore, if a planning application is likely to be refused, any urgent development 'of national importance' can be submitted directly to the secretary of state for communities and local government for planning approval."

Basing Trident submarines in the US would not be a credible long-term option, according to the report, since what is said to be one of the primary purposes of the UK nuclear force is to provide some insurance against a scenario where, for whatever reason, the US is not willing to come to the UK's defence.

"A decision to rely on a US operating base would clearly undermine the credibility of the UK nuclear force in this scenario."

Furthermore, the nuclear non-proliferation treaty (NPT) bans nuclear-armed states from directly or indirectly transferring control of nuclear weapons to "any recipient", the report notes.

It adds: "The various challenges of relocation would probably trigger a wider national discussion in the [rest of the UK] on whether or not the strategic benefits of retaining nuclear weapons exceeded the costs involved."