What would happen in terms of defence if Scotland were to become independent?

Prof Hew Strachan, military historian at Oxford University, said the "big issue" is Nato.

Speaking to the Today programme he explained that for a small state in today's circumstances not to be in an alliance structure is "to put yourself in a situation where you are essentially indefensible".

Lt Col Stuart Crawford, who has done work on what a Scottish military would look like, believes the Scottish National Party's "current policy of either negotiating their way out of Nato or not joining it is bonkers".

He told James Naughtie that it "lacks credibility" militarily and politically and "basically hands the opposition parties to the SNP a big stick to hit them over the head with".

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