Scotland may actually leave the UK. YouGov, which has long been more sceptical of a Yes vote than other pollsters, now has the Yes campaign only three points from victory.

If that happens, the Better Together campaign will partly have itself to blame: it is losing the ground war to Salmond and the SNP.

The Yes campaign is winning on almost every front. It has delivered more leaflets, put up more posters, set up more stalls and knocked on more doors. This seems to support the Economist's recent contention that while the No campaign has a capable leader, plenty of money and support from business, it has few of the enthusiastic activists fuelling the SNP.

Leaflets are the main way in which voters are interacting with each campaign. Despite all the advances offered by the internet, they have still proved by far the most effective way of reaching voters. The SNP has used leafleting to reach nearly three-quarters of voters, while Better Together hasn’t quite managed two-thirds.

There are even bigger, double-digit differences when it comes to the next two most effective methods: posters and stalls. More than five out of six voters haven’t encountered either from the No campaign, while between a quarter and a third have from the Yes campaign.

These are small differences, but they matter in an election being contested at the margins.