In the matter of Scotland's referendum, there's a lot of strenuous non-negotiation going on.

Some people are spending a lot of time talking about all the things they refuse point blank to talk about. Then they hint that their position might be negotiable. Then they deny it.

Confused? That might be the general idea. It can be perplexing to listen to a minister give a speech about the things he is not prepared to discuss. It can be more puzzling still when the individual in question poses his non-argument in terms of the national interest of a state that does not, as yet, exist.

A proposed currency union would be a case in point. We hear that "it's not going to happen" until an anonymous minister says it will "obviously" happen. We hear that "the voters" wouldn't stand for it, whether it was in their interest or not. This interpretation of public opinion becomes an argument over the national interest of an unborn entity, the remaining UK.

For this negotiation by non-negotiation to make any sense, Scotland's independence has to be assumed. For the purposes of argument, as it were. Yet when they take that step, the politicians behind Better Together make some further assumptions, big ones, about existing relations between this country and its neighbours. Unionists try to hold the UK together by stressing divisions. That's tricky.

The confusion is well illustrated by the non-negotiating ministers who seem keen enough to state their negotiating positions. David Mundell at the Scotland Office works out that the SNP - and the rest of us - are not kidding over the removal of Trident. The Whitehall cynicism, that assumed a trade off between missiles and currency, can be discarded. So is a sterling union now fit for discussion?

Then Philip Hammond, the Defence Secretary, tells us that nothing can be ruled out when negotiations begin. So are we to understand that discussions on a shared currency are indeed not not (as it were) "going to happen"? Or is Mr Hammond still trying to link sterling with submarines? The same minister wants us to believe that Trident's removal is barely feasible. So how could a deal be contemplated, even if the desire existed among Yes campaigners?

With each passing month, Better Together becomes more muddled. Patently, currency was supposed to be traded for the nuclear deterrent. If that linkage fails, as fail it will, what excuse is there to refuse a currency union? A blind refusal merely shifts the argument to fresh (and fairly pointless) exchanges over the UK debt mountain. At this point, the non-negotiations become desperate.

Contrary to the usual formulation, the SNP Government has not threatened to "walk away" from Scotland's share of upwards of £1.2 trillion. Alex Salmond and his colleagues have simply stated a fact: debt issued by HM Treasury is the responsibility of the Treasury. If Westminster insists on maintaining that its part of the islands would be entitled to everything now vested in the UK, no one will challenge its title to the debt. Equally, the parties can negotiate.

Glasgow University's Centre for Public Policy for Regions makes the obvious point - though perhaps not in this language - that an independent Scotland could come out ahead in any event. By one calculation a share of debt is worth twice the value of North Sea revenues. The markets might hesitate over an alleged default - in law, it would be no such thing - but the markets might also be rather keen on a debt-free country with oil reserves. Let's be reasonable, however.

Better Together and its famously positive case collects together some lurid predictions. It would be tough for an independent Scotland to join the EU, and tough to join the Nato club. It would be denied a currency union, face the wrath of the markets, and toil to balance its books. But proponents of the Union never get around to asking - far less answering - a basic question. How would any of this be in the national interest of the remaining UK?

Simply asserting that there would be no desire to assist a foreign country if it rejects Westminster's benign paternalism sounds very like a huff in the making. A group of former military brass have claimed, for example, that Trident's removal would be "unacceptable" to Nato. The suggestion is that Scotland too would be unacceptable. The retired generals and admirals have also warned of "resentment".

If true, it's a price that's well worth paying for the removal of Trident. Nevertheless, something is overlooked in the claim. How would it be in London's defence interests for Scotland to be barred from Nato? Contrary to the claims made by Mr Hammond and others, the UK military are enduring tough times. A dispassionate observer would say they need all the allies and aid they can muster.

That isn't how the game of non-negotiation is played, of course. The Defence Minister, with some experience in rendering military personnel redundant, returned to Scotland yesterday with the usual claim that independence would cost jobs. Already he has offered, as though as a clinching argument, the observation that Trident's removal would be complicated, expensive and time-consuming. He forgot to say that his department has been ignoring the possibility for years, no doubt assuming that a deal would be struck.

Given all this, real negotiations can't come soon enough. As things stand, the obduracy displayed by Westminster ministers almost invites a response. No Trident means no currency union and that means no deal over UK debt? I'd be sorely tempted to say: fair enough. No nuclear weapons means no Nato membership? I've heard of worse possibilities. Westminster fails to grasp, it seems, that what sounds like a dire outcome in Whitehall doesn't sound half bad if other avenues are closed.

Better Together's hand has been overplayed. The desperation to identify a catastrophe at every turn for a post-independent Scotland has blinded the campaign to real problems and real issues. Unionists who say that such a country could "of course" thrive and survive do not truly believe it. Because they cannot think of independence as anything other than a disaster, they cannot supply an argument that is not hysterical. Now they face diminishing returns.

The lesson should have been learned after George Osborne's first currency intervention. Unionists can continue to parrot that a deal "won't happen", but the scepticism they suffer in return is real. Why would a remaining UK turn its back on common sense? Just because Scotland would be foreign? The UK is in the habit of embarking on long, bloody wars because of an alliance with a foreign power. This is an argument over banknotes.

Trident is not a bargaining chip: that fact is penetrating the rhetorical fog at last. The missile system explains why the argument over independence is at bottom an argument over democracy. The country that houses the hellish weapons could never achieve disarmament within the UK, no matter how it cast its votes. That could be said, is being said, about a host of issues.

Once London's ministers get a grip on reality, the talking can begin. It won't be a moment too soon.