Even during a highly technical discussion of north sea oil on the Today programme this morning, Alex Salmond managed to find room for a spot of class war. "In the 1980s, while I was compiling the oil and gas index, David Cameron was still fooling around on the playing fields of Eton," he jibed (a remark reminiscient of Gordon Brown's declaration in 2009 that "your inheritance tax policy seems to have been dreamed up on the playing fields of Eton").
The line is a reminder of the extent to which Salmond believes that attacking the Tories in general (the party holds just one of the 59 Westminster seats in Scotland) and Cameron (who is not merely a Tory but a rich and southern one) in particular, could aid his quest for independence. Cameron, who has taken the cabinet to Aberdeen today, (Salmond and his team will meet just 10 miles away) is keenly aware of this, knowingly remarking recently that "my appeal does not stretch to all parts of Scotland". It's for this reason that he has been largely content to leave the fight against Scottish nationalism to Alistair Darling, the head of the Better Together campaign and has declined Salmond's invitation to go head-to-head in a live debate. But with the referendum now less than seven months away, it would be rather odd if Cameron, as the Prime Minister of the UK and the leader of the Conservative and Unionist Party (someone, in other words, with a bigger stake than most in the Union enduring), did not speak out on the issue.
Even after the recent tightening of the polls, the No campaign continues to enjoy a double-digit lead over the pro-independence camp. One of the few factors that could help to tilt the odds in Salmond's favour at this late stage would be a significant Tory recovery. The fear of another five years under the Conservative yoke, and a government wedded to permanent austerity, could help to push many undecided voters towards independence. But if Labour is still comfortably ahead in the polls in September 2014, far fewer will fear what lies ahead. The uncomfortable truth for Cameron is that the better his party performs, the worse the chances of saving the Union become.