David Cameron and his friends are playing up the ‘threat’ from the SNP. This gamble may yet buy them a few seats – but at the expense of their own future writes James Meadway

Recent opinion polls make two dramatic predictions: that the SNP are set to win over half the votes of the Scottish electorate. And that the Conservatives, languishing for years despite economic “recovery”, are set to win the most seats in Parliament.

The two are, of course, related. For weeks, the Tory press has been shrieking about Scots berserkers. Moderate social democrat Nicola Sturgeon has been called the “most dangerous woman in politics”. The SNP “reek of fascism”. Sarah Vine, Times columnist and wife of Michael Gove, believes an SNP-Labour deal would herald a “Communist dictatorship” in Britain. Boris Johnson used his Telegraph column to compare Sturgeon to Attila the Hun and Lady Macbeth.

The Tory line is clear. David Cameron has warned that Britain must be “saved” from the SNP. And they are banging this drum for all they are worth.

The panic is, in part, genuine – a continuation of the hysteria that descended on Britain’s ruling circles prior to last year’s referendum. They believe, almost certainly correctly, that the loss of Scotland would be a mortal blow to Britain’s status as a great power. Empire would well and truly be over. The risk that the SNP and Scottish independence represents is, from their point of view, real. (Needless to say, for those of us concerned with social change across these islands, it is a huge opportunity.)

For the referendum, they had the support of the Labour Party, with Tory and Labour working hand-in-glove to defend the Union. This time round, Labour are fighting their own battles. And this reveals the extraordinary gamble behind the Tories’ plan.

The Conservatives have just a single MP in Scotland. For Westminster elections, what happens in Scotland is an irrelevance. They can say or do more or less what they like about it. They lose nothing north of the border from the attempt to terrify those to its south. If conjuring up wild-eyed, blue-faced Picts out for loot is necessary to cajole its own side into the polling booth, and away from the charms of Nigel Farage, that is of no immediate cost.

No immediate cost. Because as older heads in the Conservatives have warned, the danger for the future is immense. The closer the Tories get to victory in Westminster, the stronger the SNP’s case is for independence. And the stronger the SNP is in Westminster, the closer Scotland moves to independence.

A minority, or small majority Tory administration would be confronting 40 or more SNP MPs. The Tories are, further, committed to diminishing the role of those MPs and chiselling away at the Scottish Government’s powers and funding. Under these circumstances, Scotland would drift into ungovernability from Westminster. Its Parliament is popular and its government could claim a rock-solid mandate, both in the Scottish Parliament and at Westminster, to oppose any such moves. The march towards independence would accelerate, perhaps markedly.

But this is, as Cameron has had tetchily to point out, the Conservative and Unionist Party. It is, in a way that Labour is not, the party of the British state and of the Union that created it. It has, in its centuries of existence, been an extraordinarily successful ruling machine. Yet it is now reduced to trashing that legacy for the prospect of scraping together a few Ukip defectors. And this, in the midst of what we are continually told is an extraordinary economic recovery.

The Conservatives are a party in decline. Its membership, for the first time ever, is now lower than Labour’s. Its effective share of the vote peaked in the 1930s. The process of decline is not smooth. It is not possible to draw a line on the graph, and assume the trend will continue. It has huge resources – financial, media, historical – that its opponents lack. But what this gamble by Cameron exposes is its fundamental weakness.

The Britain of old is on the way out. It is a fading power. Whatever the outcome from next week’s vote, those conditions will not change. The Tories’ Scottish gamble may yet buy them a few seats. But it will be at the expense of their own future.