'Scottish Independence:

25 years of economic misery, say top economists." "RBS will abandon Scotland if independence wins." Yes campaign is "poisoning the well". "Power bills to rise … renewable energy to collapse … elderly care to become unsustainable."

Those are just a few of the headlines from the referendum campaign that caught my eye last week. Others suggested that BP, Standard Life, Lloyds, Tesco Bank and Scottish Widows are all getting ready to leave if Scotland votes Yes; that Sainsbury's would increase food prices; and that cross-Border pension funds would be unsustainable. We even had a new Irish dimension to the Great Scare: "Independence for Scotland Could Destabilise Northern Ireland", said the Financial Times. In other words: a Yes vote could reignite civil war.

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Pity the poor Scottish voters, diligently reading all this and trying to make up their minds. The message is clear: independence is utter madness. Scotland would become a northern version of a backward Balkan state run by a tin-pot dictator, with mass unemployment, rampant inflation, businesses and investment deserting in droves, terrorists running rampant because of lax security, and a nationalist Taliban running universities and schools. It's a wonder that anyone supports independence, let alone one-third of the population.

The old "too wee, too poor, too stupid" approach of last year's Unionism now looks positively benign; the No camp - which seems to include most of the press - has resorted to the politics of Hammer horror. It was left only to the National Institute of Economic and Social Research to point out that an independent Scotland would actually be one of the wealthiest countries in the world and that the cost of the state pension would actually be lower in Scotland. But no-one was very interested in that.

I suppose it was inevitable the campaign would descend to this level; I recall forecasting it last year. Fear was always going to be the best card for Unionists to play in a country where people are insecure, economically fragile and unsure what independence actually means. It may work; but it is pretty unpleasant.

But lo! What is this? Through dark clouds of Mordor emerges David Cameron, a shining knight who brings a new message of love. Don't go, he pleads. You may be robbing English taxpayers and dumping all those Labour MPs on Westminster, but we love our multicultural Team GB and we want Scotland to stay. It's just a pity he wasn't able to make it to Scotland to seal the deal - which allowed the SNP to call it Project Feartie. Calling on English folk to tweet their Caledonian cousins also seemed just a little desperate, given the Unionist lead in the polls.

Cameron's speech contained a hectic soup of Unionist metaphors: "fusion of bloodlines … intricate tapestry … grown together like the roots of a great tree" - with a typically Cameron addition: "We come as a brand." Well, that clinches it for me. Stand by your brand. Vote No.

I'm sure the PM is sincere in his love for Britain and his respect for Scotland's historic contribution to it. It is often forgotten that Scotland helped create the UK, and the pound, and that it is common property. But coming after this week of hard knocks, it all felt a bit like the old good cop/bad cop routine. Hard men like Vince Cable beat Scots about the head, saying RBS would "inevitably" move its headquarters to London if Scotland votes Yes - then right at the end, the door opens and here is David offering cups of tea.

The UK Government has been a bit rattled, certainly, by a drift in the opinion polls. And there is deep concern about the lacklustre Unionist campaign. As Alex Massie put it in The Spectator: "Alistair Darling's Better Together campaign seems quieter than a Stornoway playground on the Sabbath." But I think it might be a mistake to believe this emotional address was solely directed at Scotland. In fact, Cameron's speech, for all its Danny Boyle appeals to the NHS, pop culture and Nelson Mandela, was really directed at his own people: the great mass of English Tory voters who are past caring what happens in the referendum. The "shoulder-shruggers", he called them.

First he raised the old spectre of "passports at Carlisle" and having to "change money" (even though it is the Yes campaign that wants to keep the pound and the Unionist ministers who say they can't). Then we were off to "ships ambushed on the lawless seas"; "Lord Lovat on the beach on D-Day, the bagpipes playing"; HMS Glasgow steaming for the Falklands. What was all this about?

Well, I think it was about two things: one Cameron didn't mention, Trident, and one that he did, Britain's membership of the United Nations Security Council. Both could be at risk if Scotland votes Yes.

He pointed out that it was the UK that sat in the UN inner circle, not England. It does so because of its possession of nuclear weapons. If Scotland were to leave the UK, and weapons of mass destruction were removed from the Clyde, then David Cameron is warning England that its geopolitical footprint would be much reduced.

"Britain would look weak and ridiculous" as the former Tory defence secretary, Michael Portillo, put it in the Financial Times. "Having lost Ireland, then Scotland, where would the disintegration end? Sneering enemies would join up some dots to draw an unflattering picture." He means in Europe.

I think Tory anxiety is understandable but premature. They obviously haven't been reading the White Paper on independence, which not only says that Scotland would remain in the nuclear alliance of Nato, but also that "the current Scottish Government would intend to support the rest of the UK in maintaining its seat on the UN Security Council". How can that be? Wouldn't the absence of Trident rob the rUK of its seat? Ultimately, perhaps, but the White Paper says: "We would make early agreement on the speediest safe removal of nuclear weapons a priority. This would be with a view to the removal of Trident within the first term of the Scottish Parliament following independence." Now, that packs enough weasel words to fill MC Hammer's incontinence pants. Any way you look at it, Trident is going to be around for a while.

And the United Kingdom isn't going to go away, even if Scots do vote for Alex Salmond's very limited independence. Nor is identity under threat - Scots have no problem being British and Scottish now, and would have no problem being Scottish and British after independence. This is how we have been for the last 300 years. With a currency union, a common head of state, unifying institutions like the pound, the BBC, the NHS, the National Lottery, it's hard to see how different things would really be after a Yes vote, whatever the scaremongers say. The UK is dead; long live the UK.