Travellers to Scotland from England or Wales will need passports to cross the border if Scotland votes in favour of independence, according to a report in the Daily Telegraph.
A study from Professor Robert Wright, of Strathclyde University, says that in the event of independence, Scotland would need to join the passport-free Schengen area, which covers most of the EU.
As the UK and Ireland are not part of Schengen, Scotland would no longer be part of the Common Travel Area of the British Isles.
According to The Scotsman newspaper, the SNP is in favour of remaining in a British Isles passport-free zone.
But Professor Wright says a "strict interpretation" of the rules would mean "the operation of checkpoints and border guards, the use of documents (usually a passport) for border crossing and potentially the construction of a fence or some other physical barrier."
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