THE SNP leadership's proposed policy shift to back an independent Scotland's membership of the Nato nuclear alliance was last night branded a "cynical" political ploy by opponents as Alex Salmond was warned he could have a fight on his hands to implement the dramatic U-turn.

Yet, there was also strong support for the change with Jim Sillars, the former deputy Nationalist leader, endorsing it as a sensible switch, which he had been advocating for years.

Describing an independent Scotland as Nato's aircraft carrier to help protect Atlantic shippings lanes, he told The Herald: "It does not come as a surprise to me that a policy change has occurred. In opposition, you can be fairly loose on a range of policies but it's time the party leadership and members began thinking like a state."

Senior party sources were forced to deny yesterday that an edict had gone out for SNP MSPs not to talk to media but refer all inquiries to the debate that will take place at the October con-ference in Perth.

"It's nonsense," said one Nationalist after a Labour MP accused the SNP leadership of "central Stalinist control".

Lord Robertson, former secretary-general of Nato, was contemptuous of the SNP leadership's planned policy shift, saying: "This is a cynical exercise to get rid of another electoral albatross. Membership of Nato involves accepting its Strategic Concept, which clearly sets out a position and policy on nuclear defence, so countries in Nato will greet the Nationalist approach with derision."

Jim Murphy, the Shadow Defence Secretary, said the SNP plan "raises more questions than it answers and has more to do with the referendum than the defence of our country".

He added: "The SNP are making it up as they go along. They still haven't answered the basic question of why would Scotland want to separate from the Royal Air Force, British Army and Royal Navy."

The Scottish Conservatives pointed out how the SNP's blueprint involved purchasing "con-ventional submarines" and relying on the UK to train, transport and supply Scottish troops.

Ruth Davidson, their leader, said: "None of these proposals will convince the people of Scotland that we would be safer as a separate country."