Scotland Office Minister David Mundell visited the open border between the Republic of Ireland (RoI) and Northern Ireland today to see how police tackle the problem of illegal immigration into the UK.
He welcomed steps between governments on both sides of the Irish border to devise a common immigration policy to ensure that immigrants do not exploit the more relaxed immigration policies in the Republic to enter the UK illegally.
Scottish immigration policy is reserved to Westminster but the Scottish Government has persistently pressed the Home Office to allow greater numbers of migrants to come to Scotland.
A unique Scottish immigration policy would "create difficulties" and could necessitate border controls for crossings into England, according to Mr Mundell.
Border checks "are not absurd if the SNP go down the line of having a completely different immigration policy from the rest of the UK and RoI", he said.
The SNP insists that an independent Scotland "will inherit the Common Travel Area (CTA) which exists between the UK and Ireland and will remain outside of the Schengen Agreement" that ensures free travel throughout the EU.
The CTA is the root of the Irish immigration problems, according to Mr Mundell, and has led to negotiations towards a common immigration policy.
He said the CTA has meant that "it is easier to get into RoI than it is to get into the UK. Therefore there is the temptation to come into RoI.
"Because of the Good Friday Agreement there are no internal border checks on the island of Ireland so the people come into Dublin and make their way through Belfast or Larne, across to Cairnryan and into Great Britain.
"The Government is working with the Irish government to bring our entry arrangements on to the same footing and to have the same procedures in both Ireland and the UK so there isn't the opportunity for that opportunist entry into the UK."
He added: "We are trying to keep a balance because we don't want to have an internal border in the UK, and that is one of the reasons I am against Scotland being independent as I'm not clear what will happen on the border with England.
"We don't want to have internal borders in the UK. On the other hand we don't want to see a lot of people coming into the UK mainland who shouldn't be here, so it's getting a balance."
He called on the Scottish Government to explain how it could pursue "a very lax immigration policy" and then "ensure people stayed in Scotland and didn't just come into Scotland and then travel to other parts of the UK".
He continued: "The remainder of the UK would obviously have strong interest in policing that, but the situation is if you police that you make it more difficult for people to travel and therefore, if Mr Salmond wants to have that kind of policy, he can't say that there wouldn't be the need for border controls crossing into England.
"If an independent Scotland took a very different immigration policy from Ireland and the rest of the UK that would clearly create difficulties.
"There has been a lot of progress in getting common practice in the CTA between Ireland and the UK and we want to work to have a common approach, and that's where having a completely different approach in an independent Scotland would be very unhelpful."