An independent Scotland should be allowed to let individuals hold dual citizenship with the UK, a University of Edinburgh study recommends.
Allowing people in Scotland to keep their British passports would be in line with the Scottish Government's wish for a 'soft secession' from the United Kingdom, which would include keeping the Queen and sterling.
This dual approach would mirror that of Northern Ireland's relationship with the Republic of Ireland, where citizens can choose to have both Irish and British passports.
The author of the report, Professor Jo Shaw from the University of Edinburgh School of Law, believes "the questions of citizenship status and citizenship rights have received much less attention than many of the other issues which the prospect of independence raises."
She added: "It is important to start a debate about Scottish citizenship and what it means. Citizenship is the new Scotland's 'Who Do We Think We Are' moment, and so far we have not had a chance to think through what it means to be Scottish. Is it residence, birth, or descent, or a combination of all three?"
The report says that in the event of Scottish independence it would be politicians in London - not Edinburgh - who could decide who can claim to be a Scottish citizen, and to what extent.
It also warns that the current Westminster Government may break with the UK's historic tolerance of dual citizenship. Home Secretary Theresa May hinted at this stance in June, when she reminded nationalist politicians that British citizenship is decided in London. Prof Shaw called it "an attempt to polarise the debate by reference to promised conflicts".
She believes this dispute between Edinburgh and London "shows us how hard it is to fit citizenship into the standard story of independence as it is currently told."
"The Scottish Government’s take on the journey towards independence and life after independence is one of persuading voters that they can enjoy an ideal of ‘soft secession’.
"The point of Theresa May’s intervention on dual citizenship was to suggest the opposite."
According to the study, asking UK citizens in Scotland to choose between holding a Scottish or a British passport could split families.
Such a move would also have wider repercussions for all UK citizens, researchers say. It is likely that any change would apply to any individual with dual citizenship, not only those who were British and Scottish.
The study questions whether those born in Scotland, but residing elsewhere, should be able to claim the newly forged Scottish citizenship and even vote in political elections, as happens among the diasporas of many European states.
Prof Shaw said: "It has often been suggested that residence will be the defining qualification for those who will be the new Scottish citizens. But does that mean only resident UK citizens? Or what about those from other countries who are resident in Scotland, or were even born here but haven’t acquired UK citizenship?
"There are nearly 300,000 people in this group. And then there is the large group of people born in Scotland who are no longer resident here. This group is perhaps as large as one million people, and that is a sizeable figure of potential so-called external citizens, when it is set against Scotland’s current population of about 5.3m."
The report, 'Citizenship in an Independent Scotland: Legal Status and Political Implications', was funded by the European Research Council and draws upon the issues of citizenship faced in the successor states of the former Yugoslavia.
The paper explores who would qualify for Scottish citizenship in the event of a 'yes' vote in next year's referendum on independence.
Researchers say that the Scottish Government could help boost the fledgling state by having a more liberal and inclusive approach to how legal immigrants acquire citizenship than current UK law.
For example, the process of obtaining a Scottish passport for non-citizens from EU and other countries could be easier and cheaper than the equivalent UK system.