What should be made clear in the argument over the possibility of a separate Scotland becoming a member of the European Union is that nobody is saying it could not happen.

What is being said by the overwhelming majority of people who know anything about the machinations, politics and legalities of Europe is that it will at least be very difficult, will not happen automatically, and could take many years.

When Jose Manuel Barroso, the past president of the European Commission, told the BBC's Andrew Marr earlier this year that a separate Scotland would find it "extremely difficult, if not impossible" to join the European Union, he was rubbished roundly by Nationalists. Notwithstanding his knowledge of European legislation and international relations, Mr Barroso's argument was dismissed as "pretty preposterous" and "nonsense". No cast-iron evidence was employed to make the case against Mr Barroso. Instead he was accused of "sucking up" to London, and Andrew Marr was accused of bias.

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Herman Van Rompuy, the president of the European Council, the body made up of the leaders of the 28 member states, had already argued that, if a part of a member state ceases to be part of that state because that territory becomes a new independent state, treaties no longer apply to that territory. That testament seems clear. Mr Van Rompuy did not rule out the possibility of the new state applying in future. He was explaining the rules of membership and engagement, and one of them is that, if part of a member state chooses to break away from the member state, it would have to rejoin as a separate state. That doesn't seem preposterous or nonsense and, like the rules of any other institution, these are unlikely to change simply because an applicant thinks they should.

When Jean-Claude Juncker, the newly appointed president of the European Commission, was elected in the teeth of opposition from David Cameron, Nationalists hailed him as man with whom they could do business since he had said "sensible things about independence".

However, Mr Juncker hardly had his feet under the desk when he was agreeing with his predecessor and Mr Van Rompuy. Of course he would respect Scotland's decision, he said, but added that "one does not become a member of the EU by writing a letter". He has said no more states will be admitted to the EU for five years. He was not talking specifically about Scotland.

Rather, he was making the point that, instead of pursuing EU enlargement, he wanted to consolidate what had been achieved already among the 28 members. Scottish Nationalists insist a separate Scotland's application would be treated differently.

But what Mr Juncker said would be as relevant to a Scottish application as any other. And for the sake of clarity what he said was "applicant states who want to join the European Union face a complex, difficult and drawn-out period of up to perhaps five years".

Charles Kennedy, MP for Ross, Skye and Lochaber, highlighted Mr Juncker's words in the context of the Scottish referendum at yesterday's Prime Minister's Questions.

And it is to be hoped that Mr Kennedy, a committed Europhile, will be given credit for trying to inject a dose of reality into the debate. If both he and the Prime Minister believe Messrs Junker, Barroso, or Van Rompuy, should be taken seriously how can others, many of whom know little about European politics, dismiss them so easily?

How could a separate Scotland, or a part of any other member state, or any other new applicant, simply tear up the rule book? Mr Juncker has stated emphatically that the countries that have already started the application process to join the EU face a five-year wait.

Even if the application forms are in the post it is reasonable to assume from Mr Juncker's statement that Scotland would have to wait even longer.

At least 28 member states, each with their own demands, must agree unanimously to accept Scotland's application. After the horse-trading and tortuous negotiations they might very well do so. But until then Scotland's future in Europe would be fraught with uncertainty.