NOT content with seeking a piece of my mind, David Cameron wants a leasehold on my heart.

To be fair to the Prime Minister, this sounds like a better deal than Danny Alexander's poundstretcher offer – three centuries of Union, going cheap – and might even count as clever. These things are relative, though.

Mr Cameron seems to have recognised, nevertheless, that the No side in the referendum campaign might find the traditional reign of mild terror counter-productive. Repeatedly seeking ways to say that Scotland is too poor to manage self-determination, what with the blessings of Union, is liable to wear thin before 2014. Ordinary Scots might begin to take the charge of failure personally.

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The Prime Minister must also be aware of certain facts of economic life. His Coalition relaunch on Monday – how do you relaunch a sinking ship? – was a poor diversion from reality. Britain is heading back into recession. Millions of the less well-off are to be persecuted. And the public sector, so important to Scotland, is to be given more than its share of pain.

Things will get much worse before – if – they get better. So how will the boasted advantages of Union seem to Scots in the 20-odd months ahead? Better to propose, surely, that "there are important arguments of both the head and the heart that need to be made in this great debate about the future of our United Kingdom"? Better intangible things, of the heart, than harsh truths swirling in voters' heads.

It is a reasonable proposition, for all that. Mr Alexander's ludicrous efforts to "prove" that independence could cost Scots a quid while his Treasury colleagues turn child benefit into a shambles was a reminder, inadvertent and inept, that the independence argument has to be more than an auction. A debate on economics is necessary, but not sufficient. If you think of nothing but money you keep company, mentally, with a parcel of rogues.

Mr Cameron is returning, it seems, to territory explored by Gordon Brown in his various attempts to explain and defend Britishness. The Prime Minister would have the No campaign expand the slogan Better Together to the point where it begins to acquire personal meaning for every voter. In short, he poses a question of loyalties.

Scottish; British; Scottish or British; British and Scottish? Some people can define themselves – and good for them – with an alarming ease. They are "comfortable", as the cliche goes, with their nominated identities. I can easily identify myself as a Scot first and last. I can say that Britishness is, sincerely, no more to me than a matter of passports and tax codes. But what have I really said?

A statement of identity cannot preclude the possibility that others will, in honesty, make different statements. Nor will it alter the fact that there are numerous varieties of Scot. Nor will it explain, necessarily, why identity alone – leaving aside democratic and economic rights – demands political recognition. Mr Cameron is cunning. He asks me who I think I am. That's harder to state than some are prepared to recognise.

On the face of it, there should be no problem. Scots are Scots, recognised instantly the world over, with a distinct history, distinct languages, and distinct traditions in everything from literature to religion, philosophy to sport. Depending on the calculations used, meanwhile, there are somewhere between 196 and 206 sovereign states on the planet. Of these, 193 have membership of the United Nations. Explaining why Scotland should not join them is a puzzle for Unionists to handle.

On Monday, Mr Cameron invoked United Kingdom "solidarity". It is not a typically Conservative word. The Prime Minister employed it to depict the UK as a kind of mutual aid association. Then he resorted to the usual slogan: "We are stronger together, we are better off together, we are safer together".

Decipher that, and what Cameron seemed to say is that there is a choice ahead between an idea and an identity. In this version, loyalty to the UK involves setting aside the latter for the sake of the former. You wonder, though, how the Prime Minister would fare if he made that assertion in the English shires.

But then, it is Scots who force the issue. English nationalism is not yet assertive. It comes as a distant, if persistent, grumbling, generally as a reaction to what is presumed to be happening in Scotland. Most English people have no problem identifying themselves as such. The Scots say, however, that a distinction is fundamental to the well-being of a nation.

Come 2014, as Mr Cameron seems to realise, and you will be asked what you care about most. Through the blizzard of assertions over future oil output potential or banking arrangements, the choice will remain. The No campaign had best hope it has answered a question of its own by that time: what is this British identity they defend?

Strangely, or not so strangely, the SNP has chosen to evade these issues. In a speech last month, Nicola Sturgeon, deputy leader, asserted that the claim of independence hinges on democracy and social justice. "For me," she said, "the fact of nationhood or Scottish identity is not the motive force for independence. Nor do I believe that independence, however desirable, is essential for the preservation of our distinctive Scottish identity".

Speaking at Strathclyde University, Ms Sturgeon went on: "I ask you, as you make up your minds over these next two years, to base your decision, not on how Scottish or British you feel, but on what kind of country you want Scotland to be and how best you think that can be achieved."

This strikes me as self-contradictory. It could have been an argument for improved devolution and nothing more. A nationalist party attempting to dodge the question of nationhood has indeed entered strange territory.

Come 2014, however, the rest of us will not have the luxury of tactical cunning. At some point it will indeed be a matter, whether Ms Sturgeon likes it or not, of "how Scottish or British you feel". The harder thing is to say why you feel what you feel.