MORE pressure has been piled on the SNP leadership over its controversial proposal to keep an independent Scotland in Nato after a top Scottish defence analyst claimed this would lead to nuclear weapons staying on the Clyde for longer.

Dr Phillips O'Brien from the Scottish Centre for War Studies at Glasgow University, appearing before the House of Commons Scottish Affairs Committee, was asked if being in Nato would make it more likely nuclear weapons would stay in Scotland longer.

"I would say yes," he replied. "I would say if Scotland were to go independent and leave Nato, both the domestic pressures within Scotland to get them out and the strategic need of the rest of the UK to rebase them would be raised."

Dr O'Brien suggested Nato membership was central to the independence debate. He explained: "It would be easier for the rest of the UK to negotiate the security arrangement if Scotland remained in Nato - If Scotland is outside Nato, a lot of bets are off.

"That's why no-one in the US State Department and Defence Department will go on the record about this. They are very worried about a non-Nato Scotland."

Professor William Walker from the School of International Relations at St Andrews University told the committee the Americans would be involved in defence discussions should Scots vote for independence.

He referred to the 1958 US/UK Mutual Defence Agreement, which still provides the defence co-operation framework for deals such as replacing Trident.

"The missiles going up and down the Clyde are American missiles - So the Americans would be part of this discussion; you can't keep them out. I'm not saying they would drive it, but they would nevertheless be involved in the discussion and have a position on it."

Alex Salmond is facing a growing revolt over his plans to drop the SNP's historic opposition to Nato, with several of the party's MSPs campaigning to keep the current policy. The First Minister is expected to face a showdown when the issue is addressed at the Nationalists' conference in Perth next month.

Current Scottish Government policy is that an independent Scotland would seek to get rid of nuclear weapons from Faslane "as quickly as possible".

However, Professor Walker told MPs: "The immediate expulsion of Trident from Scotland is untenable and would be regarded internationally as unreasonable. On the other hand, if Scotland did gain independence, the idea of a UK base being permanently based in Scotland would also be untenable."

"My conclusion is that you are talking about phase-out and the debate should be about the terms of the phase-out: how long it would take, who would pay for it and exactly how to manage it."

While Mr Walker accepted denuclearising weapons at Faslane could happen within two years, he stressed that replicating the facility on the Clyde south of the border could take at least 20 years.

And he said denuclearising Scotland could mean the whole of the remaining UK abandoning nuclear weapons.

"If Scotland leaves the rest of the UK, that opens up the whole debate whether the rest of the UK wishes to continue as a nuclear power - at certain times in last 30 years there's been a lot of pressure against them, a lot of people in the military who believe we don't need nuclear weapons," he said.

Writing in The Herald today, Angus Robertson, the SNP's defence spokesman and author of the proposed new policy on Nato membership, insists an independent Scotland could stay part of the alliance while removing nuclear weapons.

He says: "Like the majority of Nato members, Scotland would not possess or host nuclear weapons. Indeed, we would join both Canada and Greece as Nato members who have removed them and would take the same position as our neighbour Norway that has a strong non-nuclear policy."