It is self-interest, not sentimentality, that will determine whether Scotland votes for independence in September. The annual Scottish Social Attitudes survey shows that 52 per cent would support independence if they believed they would be £500 a year better off (although this is down from 64 per cent in 2011), compared to just 30 per cent who would oppose it. But were they to be £500 a year worse off, only 15 per cent would vote for secession, compared to 72 per cent who would vote against it.
The conclusion is clear: if Scots believe that they will be richer under independence, they will not hesitate to break up the Union. The problem for Alex Salmond is that they don't. Just 9 per cent believe that they would be personally better off under independence, while more than three times as many (29 per cent) believe that they would be worse off.
It is the SNP's misfortune to be campaigning for independence at a time of falling living standards. The only time the polls showed a plurality for separation was in 1998, shortly after the devolution referendum and during the long economic boom. Were we living in less straitened times, voters might be more willing to take a leap into the dark. But if Salmond can't persuade voters that they'd be richer under independence, can he persuade them that they'd be more equal? Not at the moment. Only 16 per cent believe that the gap between the rich and the poor would be smaller as a result of secession.
Consequently, while support for independence has risen from the joint low of 23 per cent recorded last year, it still stands at just 29 per cent (three points below the level found in 2011). Around a third of voters remain undecided but, as I've written before, there is no reason to believe that they will break for the Yes side in the numbers required for victory.
The sceptics on the Union side and the optimists on the nationalist side remind us that referendums are uncertain beasts. But while true, this ignores the tendency for support for the status quo to increase as voting day approaches (as in the case of the 1975 EU referendum, the 2011 AV referendum and the 1980 Quebec referendum). Faced with the real possibility of secession, I expect a significant minority of Yes supporters to pull back from the brink.
The SNP is keen to point out that the survey was carried out between June and October last year, before the publication of the independence white paper in November, but with more recent polls showing no increase in support for independence, it is doubtful this would have made much difference.
For now, Ed Miliband, who would struggle to govern if Labour was stripped of its Scottish MPs, and David Cameron, who would become known as the prime minister who lost the Union, have no reason to lose any sleep over the outcome on 18 September.