The title of the "no" to Scottish independence campaign - Better Together - is indicative of the group's determination to make a positive case for the Union, rather than merely a negative case against secession. Alistair Darling, who launched the campaign in Edinburgh this morning, rightly rejected the argument that an independent Scotland would be economically unviable. Rather, he pointed out that both Scotland and England have more to lose than to gain from a break-up:

The truth is we can have the best of both worlds: a strong Scottish Parliament and a key role in a strong and secure United Kingdom.

It was not the case that Scotland could not survive as a separate, independent state, he said. "Of course it could. This is about what unites us, not about what divides us.

He added:

We make a positive case for staying together. A positive case that celebrates not just what makes us distinctive but also celebrates what we share.

We put the positive case for staying together. We are positive about our links with the rest of the United Kingdom, through families and friendships, through trade and through shared political, economical and cultural institutions.

We're positive about being a proud nation within a larger state and the far wider range of opportunities for our people that this creates.

We're positive about all of the identities that we share - Scottish, British, European, citizens of the world - and don't see the need to abandon any of them.

The other point that Better Together is keen to make is that the version of independence offered by Alex Salmond is increasingly indistinguishable from the status quo. An independent Scotland would retain the Queen as its head of state, the pound as its currency, and apply for EU and, perhaps, Nato membership. As Jason asked in a recent column, what kind of independence is this?

Having abandoned  his previous enthusiasm for euro membership (Salmond quipped in 2009 that sterling was "sinking like a stone" and that the euro was viewed more "favourably), the SNP leader now favours a "currency union" with the UK. Yet as Darling pointed out this morning, monetary union leads remorselessly to fiscal union (as the euro crisis has demonstrated). In other words, Scotland would end up back where it started. Why change so much (separate embassies, separate armed forces, a separate civil service) and yet so little?

Darling had little to say about the possibility of further devolution but this is a subject the campaign will need to address in the future. As Douglas Alexander has previously said, "we must be open-minded on how we can improve devolution's powers, including fiscal powers, but be resolute in our rejection of separation". So long as Salmond can spend money without having to raise it, the SNP will remain a formidable force.

Meanwhile, it appears that Salmond and the UK government are no closer to reaching agreement on the wording of the independence referendum. Cameron is still refusing to offer legal approval for Salmond's plan to hold a two-question ballot (one on independence and one on "devo max") in autumn 2014, a few weeks after the 700th anniversary of Bannockburn.

The SNP leader has now issued an ultimatum (£), threatening to hold his own poll on election day in 2015 if he fails to win legal approval for a 2014 referendum. This would be an advisory vote designed to provide Salmond with a clear mandate to negotiate for independence. It would be open to challenge in the courts but, as I've previously noted, Scottish Secretary Michael Moore has suggested that the UK government would not launch that challenge itself. If the referendum is to be held before 2015, the two sides now have just a few months to reach an agreement.