Labour leader Ed Miliband has said he would consider a controlled border with an independent Scotland if it pursued a markedly different immigration policy from a future Labour government.
Mr Miliband said erecting borders between countries is "not good for business" but that it "stands to reason" that a controlled border would be considered if the SNP is given the chance to pursue its more liberal immigration policy by Scottish voters.
The Scottish Government said it has "a clear economic rationale for growing Scotland's population", particularly workers to support the rising number of pensioners.
Mr Miliband was in Edinburgh to convince Scots to vote No in the forthcoming referendum on September 18 - a vote which would keep control of Scottish immigration in Westminster hands.
Speaking to journalists, he said: "With all of the challenges we face internationally, with all the challenges we face with globalisation and the world coming closer together, I do believe that erecting borders is not good for business."
When asked if a Labour government would consider erecting border posts with an independent Scotland, he said: "I think it's certainly the case that we would have to look at the issue of a border if you have different immigration policies.
"It totally stands to reason, because if you have markedly different immigration policies, obviously that becomes an issue between Scotland and the rest of the UK.
"But my focus is on winning the referendum."
Mr Miliband said he has no plans to scrap the Barnett Formula, which calculates how much money Scotland receives, or resolve the "West Lothian Question" and withdraw the right of Scottish MPs to vote on exclusively English issues.
Next week, he will further outline plans for greater devolution to English regions to widen the benefits that Scotland and Wales has received from devolution.
He said: "I am going to be talking a lot next week about how we have greater devolution in England, greater devolution to English local government, because I think we can learn from the successes of devolution here in Scotland.
"I think it is going to be different in different parts of the country, but I think changing the way we are governed is fundamentally important to me."
He added: "It's not just devolution for Scotland and Wales.
"There's already devolution in London that is different from devolution in the rest of England.
"I personally think that this move towards devolution is definitely the right thing for the country."
He called on Scots to reject independence and join his "mission" to bring social and economic change to the UK.
The Labour leader said there was "deep discontent" across the country, with people "crying out" for economic change.
He said that "in the face of an economy that doesn't work and a politics that is broken, some people might be tempted to vote Yes" to Scottish independence in September's referendum
Mr Miliband insisted: "There is another, better way of changing things. Our mission - economic and social change."
With less than three months to go until voters in Scotland decide the future of the UK, Mr Miliband told an audience in Edinburgh: "By saying No in the referendum, the people of Scotland can say Yes to the campaign to change Britain as a whole.
"To change our economy and the way we are governed.
"I believe the best choice for Scotland is to help us change the whole of the United Kingdom. And to do it over the next year, by electing a Labour government that can make that change happen."
Responding to the border comments, a Scottish Government spokesman said: "An independent Scotland will continue to be a member of the current Common Travel Area with the rest of the UK, Republic of Ireland, the Isle of Man and the Channel Islands, so there will be no need for border checks between an independent Scotland and the rest of the UK.
"The Common Travel Area already allows for different and independent immigration policies within it.
"And this flexibility in the Common Travel Area will enable us to implement our own design for a controlled and more flexible immigration system."
A spokesman for the pro-independence Yes Scotland group said: "In the very unlikely event of Ed Miliband becoming prime minister, he talks about making Britain a fairer and more inclusive society, yet on the other hand, plans to continue with an immigration policy that ignores Scotland's distinct economic and workforce needs.
"From being forced to drive on the other side of the road to not being allowed to watch EastEnders, no one in Scotland seriously believes the myths being pedalled by Project Fear."
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