Former GCHQ boss Sir David Omand has warned that the SNP's defence and security plans would cast “a dark shadow” over a newly independent Scotland.

He said that the SNP's anti-nuclear stance would be likely to upset the United States if an independent Scotland wanted to be part of Nato.

The SNP's demand that all nuclear weapons be removed by the end of the first parliament following independence would also create “huge practical problems”. He added: “I find it hard not to conclude that would cast a very dark shadow over all the negotiations on intelligence and security.”

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He made his comments in an interview with the Daily Telegraph in which he warned: “For any newly independent country security is going to be one of the first and most important duties. You can't be 'a little bit independent' when it comes to security.

“A newly independent Scotland, were there to be a yes vote, is going to have to take some pretty urgent measures to ensure that it is in a position to look after its own people.”

Sir David, who after leaving GCHQ became permanent secretary at the Home Office and spent seven years on the Joint Intelligence Committee, said that if it votes for independence Scotland will need time, money and good will to build its security network. He said they are all likely to be in short supply.

Time in particular will, he said, be at a premium because a country cannot afford to leave gaps in its security and intelligence.