SCOTLAND would find it politically impossible to keep Trident on the Clyde for much more than a decade after independence, a defence expert said yesterday.

Even the threat of exclusion from Nato would be unlikely to force the SNP to embrace Trident if it wins a Yes vote next year, argued John MacDonald.

The academic, who is director of a new foreign policy think tank the Scottish Global Forum, warned against a growing assumption in UK defence circles that Scotland would trade away or weaken its anti-nuclear stance in return for concessions in post-referendum talks.

But, like most experts, he believes SNP negotiators would be flexible on their pledge to ensure the removal of Trident as soon as it is safe to do so.

MacDonald said: "My sense is that the Scottish Government will agree to a Trident drawdown period - perhaps 10 to 12 years - when warheads can stay at Coulport and give the UK Government a sensible amount of time to make provision to build another replacement. Responsible politics has to prevail."

MacDonald was speaking at a conference at Glasgow University on the defence and security implications of Scottish independence.

MacDonald believes that Nato's commitment to democracy - and its membership by a number of non-nuclear states - would make it hard for the alliance to play hardball.

He said: "Will Nato actually say 'No' to Scotland if it holds firm on its Trident eviction aspiration? If Nato were indeed to hold firm and say No to Scotland which demanded to evict the UK deterrent, would the Scottish Government be that bothered? I am not convinced it would be."

The SNP, he said, had "synonimised a Yes vote and getting rid of nuclear weapons".

Going back on such a promise would be very politically risky - not least, MacDonald stressed, if the SNP get their way and enshrine a ban on nuclear weapons in the constitution of a new Scottish state.