HeraldScotland:

Not for the first time, the question of whether those born in Scotland but living elsewhere in the UK should be given the right to vote in any future independence referendum has become the subject of media speculation – this time as a result of reported discussions within the UK Government.

But what difference might expanding the franchise in this way make?

Around 2% of those living in England & Wales and another 1% in Northern Ireland were born in Scotland. That is enough to add some 900,000 names to the referendum. Alongside the four million people who are eligible to vote in Scotland, they would represent nearly one in five of all those entitled to vote.

The motivation for proposing such an expansion is that those Scots-born who live elsewhere in the UK are thought likely to appreciate the benefits of the Union and thus would vote heavily against independence.

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But what do we know about the views Scots-born folk living in the rest of the UK on Scotland’s constitutional question of? In truth, not much. They represent a small proportion of the population of the rest of the UK and thus few turn up in any regular survey.

However, one survey gives us a clue. The academic British Election Study, which undertakes very large surveys of 30,000 people at a time, asked voters on both sides of the border in May/June 2014 how they would vote in response to the question on the indyref ballot paper. The survey also identified where people were born.

As a result, we have the views at that time of 381 people who were born in Scotland but were currently living in England or Wales. That is still a relatively small number but at least gives us a broad idea of what the balance of opinion might be.

As many as 78% said that they would vote No, while 22% indicated that they would back Yes. So, while most Scots living in the UK would have backed the Union, not all would have done so.

We should remember too that at the time this survey was conducted independence was not that popular in Scotland either. The same survey found that 57% of voters in Scotland were backing No, 43% Yes.

In short, there was a twenty-point difference between the level of support for independence among those living in Scotland and those Scots-born living elsewhere.

Let us assume that 20-point difference is still in place now (but that, given that independence is now somewhat more popular north of the border, there may have been a similar rise among Scots living elsewhere too). Let us assume too that Scots living in the rest of the UK would be just as likely to vote as those living in Scotland (probably a rather optimistic assumption).

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Given that currently support for Yes in the polls is currently a little less than that for No, enfranchising those born in Scotland but living elsewhere would almost undoubtedly help turn what might be no more than a narrow unionist victory into a somewhat more comfortable one.

However, if support for independence in Scotland were to return to the 54% level it reached last summer and autumn, the votes of those living elsewhere in the UK might not be sufficient to delivery victory for the Union. The overall outcome might still be a 50.4% vote for Yes.

Enfranchising Scots living elsewhere might make it somewhat easier for Boris Johnson to save the Union – but it could prove an inadequate bulwark if Nicola Sturgeon can recapture the mood that prevailed north of the border not so long ago.

John Curtice is Professor of Politics, Strathclyde University, and Senior Research Fellow, ScotCen Social Research.