THERE is "no guarantee" that there would be a common travel area between an independent Scotland and the rest of the British Isles, Alistair Carmichael has insisted.
He addressed the issue as he published the latest Whitehall analysis paper, which extols the virtues of the UK's current system of border management.
The SNP Government argues that, unlike other new members of the European Union, an independent Scotland would not sign up to the Schengen Agreement - the passport-free zone which covers almost all of the EU - but would continue to have a common travel area with the rest of the UK and Ireland.
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However, fears have been raised that, to prevent an independent Scotland, with a different immigration policy, becoming a soft entry point to the rest of the UK, border posts would have to be set up between England and Scotland.
This assertion was dismissed out of hand by the SNP as "scaremongering".
Mr Carmichael said: "We have got a system that, for all its occasional difficulties like any other bureaucracy, is fundamentally sound and gives people in Scotland, as part of the UK, a measure of security."
He added: "Something we have is good. For those who want to take us away from that, it is for them to explain why what we would have (under independence) would be better."
In response, Nicola Sturgeon claimed the latest paper "from the Project Fear library lacks all credibility", ignoring the Coalition's 22% staff cuts to the UK Border Agency as well as the Scottish Government's own proposal for a Scottish Border and Migration Service.
The Deputy First Minister said: "The only people wanting to erect borders are Mr Carmichael's own colleagues in the Westminster Government, who are threatening to drag Scotland and the UK out of the EU and the single market.
"It's time for less Project Fear and more common sense."