Shadow Chancellor Ed Balls has claimed it is “inevitable” that border controls will be put in place if Scotland becomes independent.
The Labour MP said Westminster would be forced to take action because the Scottish Government was pursuing a different immigration policy.
Mr Balls, who was in Edinburgh yesterday to campaign against independence, warned that cross-border trade and mobility of people would “suffer”.
SNP external affairs minister Humza Yousaf recently claimed healthy population growth was “vital for economic growth”.
He claimed a “yes” vote would provide an opportunity to tailor a robust new approach to migration to address Scotland’s social, economic, educational and demographic needs.
The Scottish Government insists there would be no need for passport controls and the country would remain part of the common travel area.
But Mr Balls, who claimed First Minister Alex Salmond was trying to “con” Scotland into voting for independence by refusing to reveal his currency plans and transition costs, disagrees.
“If you had different immigration policies for Scotland and the rest of the UK, the approach taken is to have border controls,” added the Labour MP.
“If Alex Salmond makes a virtue of changing immigration policy, the view that would be taken in the rest of the UK is if a different country chooses to go down that road there would have to be checks across the border.
“I think that is inevitable, it is bad and not what we want but I think it is where things will end up.
“In the end trade and mobility will suffer.”
A Scottish Government spokeswoman insisted there would 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 policy within Ireland and the UK, the Isle of Man and the Channel Islands,” she added.
“This flexibility in the common travel area will enable us to implement our own design for a controlled and more flexible immigration system.”