So now we know the last Tory trick in their book. They’ve tried all the standard pre-election routines. We’ve had promises of tax cuts, naturally. They’ve offered a discounted right to buy on housing association homes they don’t own. The party of austerity has sprayed around spending pledges, while ridiculing Labour as incompetent spendthrifts. A cabal of City-funded multimillionaires has tried to paint themselves as the “party of working people”. They’ve claimed to be presiding over a great economic revival.

But the numbers won’t budge. They dismissed Ed Miliband as hopeless, but his ratings are climbing.

So now they’ve fallen back on a brazen attempt to inflame English nationalism and turn Britain’s peoples against one another. Cheerled by a Conservative press largely owned by tax-dodging overseas plutocrats, the Tories claim the English would be held to ransom under a Miliband government dependent on SNP support. The Scots, who were begged to stay in the union during last year’s referendum, are now portrayed as some kind of foreign menace.

The former prime minister John Major, who was himself held to ransom by Ulster Unionists and Eurosceptic MPs, has claimed an SNP-backed Labour government would face “blackmail”. The SNP leader, Nicola Sturgeon, is denounced as “the most dangerous woman in Britain”. There’s even talk of an SNP “coup” and “fascist intimidation”.

This is all fantastical and anti-democratic nonsense. Some of it is no doubt rubbing off south of the border, where the Tory tactic is specifically aimed at winning back English nationalist Ukip voters. But those who claim to treasure a united Britain can’t have it both ways. Either Scotland is part of the union or it isn’t. If it is, whoever Scottish voters elect has the same right to play a part in Westminster politics as any other party.

No wonder the Tories themselves have fallen out over the issue, with genuine unionists such as the former Scottish secretary Lord Forsyth accusing the prime minister of playing a dangerous game. If the game is successful, and the Tories are returned to Downing Street, that will provide by far the most fertile ground for a new referendum on Scottish independence to be held and won.

The reality is that, on current polling, either Miliband will become prime minister with SNP support – or there will be five more years of Cameron. That’s a bitter pill for Labour in Scotland to swallow, and if the party can pull back a few seats from the expected SNP landslide, it will strengthen Miliband’s hand. But the rise of the SNP, which has determinedly positioned itself to Labour’s left, is the product of 20 years of New Labour politics and an anti-establishment tide across Europe that has swelled since the 2008 crash. The Sun’s claim that the SNP is “hard left” is crazed. Sturgeon has understandably been taken to task over privatisations and spending squeezes in Scotland.

But the SNP ship has sailed. And the idea that nationalist support would make a minority Labour government “illegitimate” – let alone that this would be the first time such a thing has happened, as Cameron claimed at the weekend – is ridiculous. Minority and coalition governments dominated the first half of 20th-century Britain. Governments dependent on Irish nationalist support were common in the years leading up to the first world war. And Labour governments have regularly relied on the Irish nationalist SDLP, even though the party wants to “break up the UK”.

Cameron wants to make austerity permanent. The only alternative is a Miliband government

You’d never know from the anti-Scottish fearmongers that Sturgeon is now the most popular party leader in Britain – when English and Welsh voters were exposed to her in the leadership debates, many liked what they heard. Nor would the SNP’s negotiating hand in a hung parliament be as strong as claimed, given the party’s commitment to vote down a Tory administration in any circumstances. And Cameron’s Conservatives would themselves very probably have to rely on Ukip and Northern Irish DUP votes, as well as his own right wing, if their scaremongering were to take them over the line on 7 May.

But all this is a diversion from the fundamental choice at the election. That is between a Cameron-led government, which has presided over the deepest cuts in the living standards of the poorest for over a century while slashing taxes for the rich, and which now wants, in his own words, to make small-state austerity “permanent”. The only alternative is a government led by Miliband, committed to ditching the bedroom tax, clamping down on zero-hours contracts and non-dom tax status, abolishing the House of Lords, introducing mansion and bankers’ bonus taxes, and raising the top rate to 50%.

For all Miliband’s compromises over austerity, the distance between the main parties is wider than is often understood. That’s partly Labour’s own doing. As the Institute of Fiscal Studies points out, there is little difference between the SNP’s “anti-austerity” spending pledges and Labour’s “triple lock budget responsibility” plans, which in fact would allow Miliband to avoid almost all cuts.

But Labour leaders give the opposite impression, to appease the City and potential swing voters fed years of economic mumbo-jumbo by politicians and the media. The danger is, that message alienates Green voters and others Labour needs to win back to be able to form a government – just as Cameron is fighting to deflate Ukip support. On the doorstep in Nick Clegg’s Sheffield Hallam constituency on Friday, no one raised the Caledonian menace with me. But police employees who a generation ago would have been solid Tory voters were enthusiastically backing the Labour challenger.

Which underlines Cameron’s problem: however much he trumpets recovery, the reality of cuts, job insecurity and years of falling living standards have taken their toll. Against that background, the prospect of a minority government dependent on other parties committed to change is hardly so terrifying, let alone illegitimate.

There are plenty of downsides, including the risk of spatchcocked policies and endless haggling. But multiparty alliances, informal or otherwise, also offer the prospect of opening up politics to pressure from those who have been locked out of the system – inside and outside parliament. In any case, some such arrangement now looks almost certain. The only question is which party and prime minister will be at the centre of it.