THE story of voter engagement is told in two polling statistics, both of them coincidentally standing at the figure 68%.

That is the percentage of Scots voters who told TNS BMRB they had heard of the recently published White Paper on independence.

Coincidentally, it was also the percentage of respondents who were aware of it and, when asked how much influence the information in the document had on their referendum voting intentions, replied "None".

The former is unsurprising. Given the blanket coverage of the launch across all media, you might have expected people to at least have heard of it. But the latter response is unsurprising too, since Scotland's Future is the same size as a Harry Potter novel but with fewer plot twists. In an interview with this newspaper yesterday, Deputy First Minister Nicola Sturgeon was impressed by the level of public engagement with the document which was "going like hotcakes" in all its formats - traditional hard copy, browsing on-ine and via e-book download.

She is pinning her hopes on it being the undecideds who are fuelling this interest. Her problem is that it may involve mostly those already firmly in the Yes camp. If that happens, the current modest closing of the polling gap between No and Yes may stall. But if Ms Sturgeon is right, the current trend may continue and make for a fascinating endgame.

The latest poll suggests that among committed voters over the last three months, the campaign for a No vote has shed around five points to stand at 45%. The Yes vote has crept up a couple of faltering points to 30%. But if this became a trend (a very big if) over the next six months you could easily end up with the two sides neck-and-neck going into the final campaign proper. A few weeks ago that was unthinkable. This may explain recent acrimony and back-biting between different parties in the Better Together campaign.

Ms Sturgeon is pinning her strategy on the White Paper being a slow burn, an encyclopaedic resource into which undecided voters will increasingly dip to satisfy their curiosity about the possibilities of Scotland as an independent nation. In an era of low turnouts and political disengagement, that seems almost heroically high-minded and, in its way, admirable.

The White Paper by no means answers all the questions about Scotland's finances, our place in Europe and other institutions, and our future currency options. But it provides a narrative for a journey towards a different future and, as the Deputy First Minister ceaselessly points out, there is no equivalent document on the other side. Whitehall's prodigious output of Scotland Analysis documents offer a steady diet of argument as to why independence would be bad and continuing in the Union would be good. But unlike the White Paper, these can never even attempt to paint a picture of what a future UK might look like. because that campaign is a product of divided visions. On that, Ms Sturgeon is correct. There is, as yet, no blueprint on the other side.