Analysis: The really burning question now is the question itself

But there are key differences between last year’s referendum and the independence ballot. Unlike AV, Scotland’s constitutional future is a subject with which many voters are familiar and on which they already have views. Moreover, for many those views are a reflection of a sense of a distinct Scottish national identity. In these circumstances opinion is unlikely to be moved simply by running a relentlessly negative campaign.

Second, although the Yes side may be behind in the polls, it is far from clear that all that Scotland wants to do is to say, ‘No’, and then let that be the end of the matter. Among those inclined to vote against independence, at least half are not adverse to Scotland having more autonomy within the UK. Those voters will need to be given a positive vision of how their wish for more autonomy can be acknowledged within the Union.

Still, might not unionists be at risk of confusing voters, inviting them to say Yes by voting No? That presumes that Mr Salmond’s proposed referendum question, which invites voters to say Yes or No to Scotland becoming an independent country survives the scrutiny of the Electoral Commission. Some unionists argue the referendum should ask voters to say Yes or No to the Union. That seems unlikely. But following the referendums on mayors in England last month, voters may be asked to choose between independence and the Union rather than between Yes and No.

• John Curtice is professor of politics at Strathclyde University