Scotland benefits considerably from the United Kingdom's approach to immigration and border security, according to the latest piece of pro-union analysis from the British government.
The paper which focuses on the theme of borders and citizenship is the tenth in a series from the government on potential Scottish independence.
It said the UK's visa system is designed to ensure only those with the skills the economy needs are allowed to migrate to Britain.
"But within this unified system Scotland's particular circumstances and need for skilled labour are addressed. There is a separate list drawn up by experts, based on evidence from employers and the public, of skills which are short in Scotland," the report said.
Deputy first minister Nicola Sturgeon was critical; and sent an open letter to Scottish secretary Alistair Carmichael in response.
She said: "This latest paper from the Project Fear library lacks all credibility. Firstly, it ignores the 22% staff cuts that the UK government is making to the UK Border Agency and the Scottish government's own proposal to establish a Scottish Border and Migration Service.
"And secondly, it completely ignores the reality of the Common Travel Area, in which the UK and Ireland already have no border controls but differing immigration policies.
"Thankfully, people in the rest of the UK are far more reasonable than Mr Carmichael and his colleagues, with polls showing that the vast majority would expect their government to work with an independent Scotland to ensure continued co-operation within the Common Travel Area."
Sturgeon's comments echo those made by the Scottish government's White Paper on independence, which said the interests of Scotland would be best served by a green card immigration system.
Meanwhile, the latest Scottish Social Attitudes survey showed that the prospects for the Scottish economy were far more important to voters then membership of the EU or keeping the pound.
Responding to the findings of the survey, Carmichael said: "The future of our economy is central to the referendum vote and the arguments are firmly on the UK's side. As part of the UK, people can count on having the UK pound and the Bank of England as lender of last resort.
"Leaving the UK would throw all of that into doubt as well as placing the financial burden of creating a new state from scratch onto the Scottish taxpayer.
"People want to be absolutely sure of what leaving the UK would mean for them in terms of their prosperity. Staying in the UK will allow us to continue pooling resources and sharing risks, while leaving would open up a far smaller Scottish economy to volatility in its annual revenues."