ALEX Salmond has insisted an independent Scotland would seek to trade in Britain's Scottish-based nuclear arsenal for "something more useful" as part of a prolonged negotiation with the UK Government.

The First Minister made the comment as he endorsed the move by his SNP colleague Angus Robertson, the party's defence spokesman, to ditch the Nationalists' long-held opposition to an independent Scotland joining the Nato nuclear alliance – provided Trident missiles were removed from Scottish soil.

"The nuclear weapons concerned are not Scotland's nuclear weapons," Mr Salmond declared yesterday. "If they are regarded as an asset, which I would find difficult to regard it as, then I am quite certain we can trade that asset for something more useful."

Nick Harvey, the Armed Forces Minister, recently told MPs that resiting Britain's nuclear deterrent to England would be possible but would also be fraught with difficulty. "It would be a very challenging project, which would take a very long time to complete and would cost a gargantuan sum of money," he said.

Insisting relocation of Trident would be the biggest issue in any post-independence negotiations, the minister stressed that if UK taxpayers had to pick up the decommissioning costs, then "their ability to pick up any other bills would be proportionately diminished".

The SNP has previously made clear an independent Scotland would wish to see the removal of nuclear weapons from Scottish soil "as quickly as possible" but no specific timescale has ever been given.

As the Holyrood Government's political opponents continued to pour scorn on its U-turn on Nato membership, the First Minister turned his fire on Lord Robertson, former secretary-general of the nuclear alliance, who yesterday branded the SNP leadership's move "a cynical exercise to get rid of another electoral albatross".

Mr Salmond referred to the peer's comments that the Nationalists had to accept "Nato is a nuclear alliance and members will retain nuclear weapons".

However, the First Minister noted: "When he actually was Nato secretary-general in a speech to the Moscow State Institute on Foreign Relations from February 21, 2001, Lord Robertson said in the founding act, Nato committed itself to the famous three nuclear noes: No intention, no plan, and no reason to establish nuclear weapons storage sites on the territory of new members; a commitment still valid.

"Clearly, Lord Robertson's memory is escaping him. What he is saying about Scotland seems to be different to what applies to 25 out of 28-member countries in the Nato alliance."

Mr Salmond added: "Times change. Circumstances change. The resolution sets out a very carefully positioned statement, which shows a willingness to co-operate with our friends and allies but makes clear the non-nuclear position of the SNP is paramount."

Earlier this week, when Mr Robertson was asked why a party and a government, which was anti-nuclear, now supported an independent Scotland becoming a member of an organisation protected by a nuclear deterrent, he replied: "That's not what we are seeking.

"What we are seeking is the same membership as member states, including Norway, currently have; that's a focus on coventional defence co-operation, training and operations."

Last night, Ruth Davidson, the Scottish Conservative leader, accused Mr Salmond and the SNP of a "startling turnaround" given their opposition to Nato membership had stood for 30 years. "Alex Salmond's support of this motion is nothing to do with defence, an issue on which he is continually exposed as weak; it has everything to do with the referendum.

"He's terrified at what the people of Scotland think about his vision for separation and is watering down every policy he can think of," she added.