Is there some specific reason Scotland would have to have a different currency? Does the UK government restrict the use of the GBP to the UK alone? I know the USD is the official currency of more than just the US (East Timor, El Salvador, Ecuador, and one of two officials in Panama), is that not possible with the GBP?
It's possible, and the Chancellor's talking out of his arse when he says the Scots can't use it - I don't think the US had any involvement when Ecuador decided to scrap the sucre and convert to dollars. Or they could just keep printing Scottish money and peg it to the pound at a 1:1 ratio, which'd have about the same effect. China pegged the Yuan to the dollar for ages and it didn't hurt them in the slightest.