An independent Scotland that is part of the European Union will need to build a "great wall of Gretna" at the English border, the UK immigration minister has warned.
Kevin Foster said a separate Scotland that was part of the Schengen scheme, which permits free travel without passport checks between European nations, would necessitate the construction of a hard border with England.
Speaking on a visit to Scotland, the Home Office minister challenged Nicola Sturgeon’s party to "start being upfront about the impact of some of their policies".
Ms Sturgeon floundered during the election when pressed why a separate Scotland would be the only part of the EU not to have a hard border with a neighbouring country that was not part of the bloc.
Around 60 per cent of Scottish exports go to the rest of the UK – more than three times the value of those that go to the continent.
Speaking in Linlithgow, West Lothian, Mr Foster said: "If they wanted Scotland to join Schengen, that does mean a hard border, it means building a great wall of Gretna."
He said the SNP should be "getting on with the day job" of dealing with coronavirus and recovery from the pandemic rather than "debating the philosophical future" of the country with another independence referendum.
Mr Foster also dismissed the Scottish Government’s calls for more powers over immigration to be devolved to Holyrood.
He said: "We’re very clear that we need to have a migration system that works for the whole of the United Kingdom.
"What I am not interested in doing is creating passport control at Berwick. The UK operates as a single market despite the SNP’s thoughts on this."
An SNP spokesman said: "People in Scotland are fed up with Tory ministers coming here on day trips spouting nonsense as part of their anti-democratic campaign to tighten Westminster control over Scotland.
"Just like Ireland, people in an independent Scotland as part of the EU would have the huge advantage of being able to move freely across the British Isles as well as the EU – instead of being subject to Boris Johnson’s disastrous hard Brexit."