Today Better Together launches a new "positive" advertising campaign.

"Scotland can have the Best of Both Worlds," billboards will proclaim, "a Scottish Parliament with more powers guaranteed - and more opportunities as part of the UK."

Importantly, it doesn't contain a single morsel of negativity. The "best of both worlds" pitch has always been a good one, so good in fact at one point last year the SNP tried to co-opt it; not only is it positive, it captures the constitutional dynamic of devolved power within the UK.

Indeed, it's worth remembering that when the pro-Union campaign began in earnest at the beginning of 2012 it accentuated the positive at every turn. During a speech in Edinburgh the Prime Minister set out an upbeat vision of the UK, celebrating its political, historical and cultural diversity.

Since then, however, Better Together's metanarrative has suffered. Unlike them, Yes Scotland understands a positive overarching message enables lots of negativity underneath, thus its vision of a thriving independent Scotland vis-a-vis a UK it depicts as decrepit and past its sell-by date.

Last year's warning that mobile phone roaming charges would apply post-independence was a turning point. Given the EU was preparing to phase them out altogether, this appeared silly, fuelling Yes Scotland's broadly-applied charge of "scaremongering". So now, even when the pro-Union camp has a demonstrably stronger case (ie international aid, currency, etc), it still comes off worse.

There has also been complacency, despite persistent claims to the contrary. For too long the No campaign has operated on the assumption the truth will out, and while credibility is key, so too is messaging, rebuttal and overall tone. On the last three points Yes Scotland has proved formidable, and also remarkably disciplined compared with the too-many-cooks demeanour of its opponents.

To be fair, Better Together suffers from the generally appalling level of the wider debate. Anyone who regularly engages with the "indyref" debate on social media would have found Hilary Mantel's comments depressingly recognisable: "To a large extent," she said, "proper political debate and activism has been replaced by illogic, by platitudes. And actually a lot of it is just abuse and bullying."

So while there continues to be no shortage of "debate", thus far it's been a triumph of quantity over quality. Take, for example, a recent publication called simply Scottish Independence (in a series optimistically entitled Great Debate), featuring arguments for and against independence by, respectively, the columnists George Kerevan and Alan Cochrane. In many respects, it is a microcosm of the wider constitutional debate.

Kerevan is firmly in the unequivocal school of nationalism, repeatedly asserting what an independent Scotland "will" or "would" do, only occasionally allowing qualifications like "could" or "might" to creep into his 87 pages. My favourite was a line asserting an independent Scotland "will ban commercial banks from proprietary trading". This, I suspect, will come as news to Business for Scotland, not to mention the banker-friendly First Minister.

There's also the usual blend of sub-Nairnite analysis (the UK is invariably described as "ramshackle", "failed" or "decaying"), Thatcherism (independence, argues Kerevan, would tackle Scotland's "dependency culture") and Salmondism (neoliberalism is bad, except in a Scottish context), conveniently concluding any healthy bits of the Scottish economy have "nothing to do with the Union" while all the negative ones do. An independent Scotland, concludes George, will "favour" the "ambitious, educated, entrepreneurial" - the reader is left wondering what will happen to everyone else.

The most tortuous chapter blends religion and philosophy to argue the Scottish psyche is rooted "in a profound moral argument"; "a distinct moral outlook" remaining "embedded in the nation's cultural DNA". It is the "suspect moral universe" of the UK, therefore, that Scotland "seeks to escape through independence". Naturally, Kerevan inserts a redundant caveat denying any "claim for Scottish moral superiority" while taking care to point out none of it should "be interpreted as a call for intervention in the market place" (God forbid).

Alan Cochrane, meanwhile, thinks this view of Scotland "borders on racist", but while I'd like to critique the book's case against independence, in truth there isn't much to analyse. In just 46 pages the Daily Telegraph's principal (and very fine) Scottish columnist takes many familiar pot shots at nationalist arguments but at no point advances a compelling case for the Union.

Indeed, many on the No side of the debate have revealed themselves to be pretty ineffective Unionists. Asked why the UK was "better together" all International Development Secretary Justine Greening could offer was "I don't know why it works, like a wine…but somehow it does". This inadequacy is mirrored in another context: it's been quite striking to watch Nick Clegg - a former Eurocrat and MEP - struggle to defend the UK's place in the EU beyond highlighting the obvious flaws in the Faragist vision.

It is of course difficult - but not impossible - to frame a "No" vote in positive terms. Better Together might do well to study the Ukip playbook (not, obviously, in policy terms), particularly its 2004 European Parliament election campaign in which it prefixed its messaging with "Say No to…", a "positive negative", if you like, rather than the more straightforwardly negative "No".

Perhaps Better Together is already conscious of the need to reframe its pitch. In the next few weeks former Prime Minister Gordon Brown will publish My Scotland, Our Britain which will seek to defend the status quo in more positive terms, while this week, according to a press release, he'll be "making the positive case pensions are more secure as part of the UK".

This Easter rebranding obviously has to go beyond simply punctuating everything with the word "positive". That said, perhaps the No campaign is just confident what Nixon called the "silent majority" remain on side. It brings to mind the 1992 General Election when the SNP appeared to have all the momentum while polls showed majority support for independence, yet come polling day - although its vote increased by 7% - it won just three MPs.

But even if that scenario applies later this year I can still detect uneasiness in the pro-Union camp. On Saturday the New York Times quoted Alex Salmond saying there was "a hysteria of potential loss of possession impinging on the minds of the British establishment", and although over-stated, the First Minister had a point.

And it's an existential discomfort also fuelled by Euroscepticism. With that in mind it's not impossible David Cameron, already weakened by a strong Ukip showing in next month's European elections, doesn't become the Prime Minister who "lost Scotland" but the leader who nearly lost Scotland, and from his point of view - particularly with a General Election just months away - that might be almost as bad.