'I think there's a credible chance we'll lose," one Westminster adviser told me back in April 2012.

"It's an understatement to say I'm not taking this for granted: we really might lose this."

And so, more than two years later, they still might. "No complacency" has been a Better Together mantra for some time now, and yesterday's polls illustrate why.

First, a mea culpa: about two years ago a Yes Scotland strategist told me that once Scots started considering properly the choice before them - as in April/May 2011 - they'd move to Yes. "The ground," he remarked, "is the most fertile I've ever encountered."

I have to admit I was cynical. The 2011 Holyrood analogy struck me as imperfect, after all a referendum is a higher-order decision, but then of course the Yes campaign has fought the referendum like an election campaign, majoring on mood, policy and momentum rather than realism, principle and detail. Labour has responded in kind.

Thus Nicola Sturgeon's opening statement in last week's refreshingly even-tempered STV debate, which sounded the 1979, Tory and even Poll Tax claxons loud and early; she knew which buttons to press. Likewise, with the NHS privatisation tactic: deeply cynical, given its tenuous connection with political reality but, nevertheless, clearly effective.

The onward march of Yes is all the more impressive given the weakness of many of its central arguments: the proposed currency union and social democratic nirvana funded by tax cuts should have been easy for Better Together to pick apart (and to be fair they've tried) but, given the early framing of the debate as "hope" versus "fear", this proved harder than they expected.

What of yesterday's unionist response? A relatively restrained Alex Salmond called it a "panicky last-minute measure" and he was half right: it was self-evidently forged in a panic but the "measure" itself wasn't new, just placed on an escalated timescale. George Osborne (a curious messenger), meanwhile, basically reheated his carrot-and-stick strategy (more powers and the currency threat); a plan of action is due to be unveiled on Wednesday.

It will undoubtedly be a hard sell. Judging from certain briefings, it has been pitched as a "federal" settlement for Scotland within the UK, inviting ordinary Scots to help shape a new devo-settlement that'll form part of the first Queen's Speech after next year's General Election. Now that might be many things (and it ought to gladden my born-again federalist heart) but it isn't federal - although even inaccurate usage of the "f" word represents a major shift in Westminster thinking.

Better Together will then sell that proposal (in whatever form) in "five or six different ways" in the short time left till polling day. Despite an initial knock from the first YouGov poll, confidence in the No camp remains surprisingly high: they still think there's a gap between those two polls and what's happening on the ground (as evidenced by canvass returns and postal votes), while they're confident heads will follow hearts as undecided voters make up their minds. They point out, rightly, that while many Labour voters will vote Yes, so too will many SNP supporters vote No.

But even if Better Together manages to secure victory on September 18 (and if events follow the Quebec pattern in 1995 there could be a rebound that favours No) neither the Union nor the Labour Party will be left with much breathing room. To be frank, over the last couple of years Better Together has never looked particularly "together", while in fashioning a "No, but" offer the People's Party frequently prioritised internal machinations above the wider battle.

It is unusual, in other words, to find the Tories more united and coherent on the constitution than the historic party of Home Rule, but then stranger things have happened. And if there is a close No, a decisive response from the three unionist parties will move from possibility to necessity. And by that I don't mean yet more ad hoc devolution - the returns from that strategy diminished long ago - rather, a comprehensive, holistic settlement that also deals with the (English) elephant in the room.

Of course, this can be dismissed as constitutional fantasy, but if unionists are serious about saving the Union then I've wracked my increasingly weary brain for an alternative and I can't think of one. The blueprint exists, most recently set out in Gordon Brown's book, My Scotland, Our Britain, (the contents of which are better than its title); all that's required is the cross-party will to execute it.

That is, make no mistake, a big political ask and therefore unlikely. So easily distracted by a pretty miserable foreign policy backdrop (understandably), John Bercow's administrative woes (less understandably) and a bloody by-election in Clacton (infuriatingly), Westminster has - not for the first time - taken its eye off the ball. Only now is it taking something seriously that should've been considered so from the beginning of 2012.

But if unionists have been guilty of complacency, many Yessers must be witnessing a shift they didn't seriously expect to transpire. Faced in less than two weeks with the prospect of seriously challenging independence negotiations, I'd be curious to know just how prepared the Scottish portion of Her Majesty's Civil Service is. Their task, should it come to pass, is daunting.

More to the point, narrowing polls don't suddenly transform clever debating points into realistic policy. Recent history is littered with the inevitable detritus of "positive" centre-left campaigns (Messrs Obama and Hollande spring to mind), and there remains a sizeable gap between what is being promised by many in the Yes camp and what is deliverable even in the medium-to-long term.

While it's easy to admire shrewd, disciplined campaigning, the repackaging of orthodox neoliberalism as social democracy, tax cuts as a competitive advantage, and regressive policies as somehow progressive remains colossally dishonest. Excitable Guardian columnists may interpret the desire for independence as a means of escaping neoliberalism but that doesn't make it so. Rooted in the often-unpleasant status quo, Better Together was always going to struggle in that particular bidding war.

Indeed, one of the most irresponsible by-products of the referendum debate has been the belief that somehow there exist easy solutions to incredibly complex problems. Fantasy politics might win a referendum campaign, but it's hardly an effective way to begin life as a new (or rather old) state. For all the regal handwringing in yesterday's Sunday Times, who might be head of state would actually be among the least of an independent Scotland's concerns.

As Fintan O'Toole argued elegantly in the Sunday Herald, "sovereignty" is far from meaningless but also heavily constrained - even more so today than in the fledgling years of the Irish Free State. Sure, Salmond and his deputy frequently acknowledge that independence isn't a magic wand, but such a caveat is as glib as it is inadequate. Back on planet earth there exist significant challenges no matter what the outcome.

That said, for Yes to be within touching distance of victory is an incredible achievement - even journalistic cynicism can't detract from that.