It’s forty years since anybody has won power in a UK general election without the backing of Rupert Murdoch. He’s not happy about the prospect. That’s the explanation for the surreal juxtaposition of the Sun covers from England and Scotland:

‘Vote Cameron!’ ‘Vote Sturgeon!’ It makes no sense, unless you see that what it’s really saying is ‘Vote Anyone But Ed!’ Miliband took an early decision to attack Murdoch, and as a result owes him nothing. To have people in office who don’t owe him is not Murdoch’s happy place.

Hence too the cover of today’s Times: ‘Miliband asks unions to save his No. 10 bid.’ The first reaction to that of anyone who knows anything about the UK constitution (such as it is) is: eh? What? The unions play no role in forming the next government, as the Times knows perfectly well. It also knows that the idea of unions choosing the next government is provoking for right-of-centre voters. The idea it’s trying to plant is that Miliband, if he comes second in the popular vote, has no right to be in Downing Street. The hook for the story – to do with internal Labour party rules – is slight. No matter. Yesterday’s Times leader was beating a similar drum. ‘Occupy Downing Street,’ it advised Cameron. ‘If Ed Miliband tries to oust David Cameron from No. 10 with SNP support the public will cry foul. The prime minister is right to say that he will stay put.’ The leader spoke of ‘Conservative signals at the weekend that Mr Cameron plans to stay in No. 10 even if he has no overall majority.'

This is part of an emerging theme, in which voices on the right are starting to say that Labour can’t form a legitimate government unless they are the largest party. In turn, voices on the left arestarting to talk about a ‘coup’, in which ‘the Conservative press are lining up to push Cameron into Downing Street even if most of the UK has just voted to sack him.’ The headline of that interesting piece by Adam Ramsay, on the OpenDemocracy website, was: ‘The newspapers are preparing for a coup, and Labour is doing nothing to stop them.’ Owen Jones puts it like this in the New Statesman: ‘If the Tories get more seats than Labour, get ready for a Very British Coup.’

How would that work? Here’s the relevant passage from the Cabinet Manual. (Other countries have constitutions. We have something which sounds like a how-to book about cupboards.)

2.12 Where an election does not result in an overall majority for a single party, the incumbent government remains in office unless and until the Prime Minister tenders his or her resignation and the Government’s resignation to the Sovereign. An incumbent government is entitled to wait until the new Parliament has met to see if it can command the confidence of the House of Commons, but is expected to resign if it becomes clear that it is unlikely to be able to command that confidence and there is a clear alternative.

So Cameron would have first dibs on getting to 323 seats. The maths will be relatively simple, the politics less so; but he’ll know fairly soon whether he can get there or not. If he can’t, he’s out, though the Manual says that he can stay until Parliament gets together again on 18 May. It would be helpful for our democracy if the language here were a little more forceful. Look at the exact wording: ‘expected to resign if it becomes clear that it is unlikely to be able to command that confidence and there is a clear alternative’. ‘Expected’ is weaker than ‘obliged’, ‘unlikely’ offers wiggle room, and as for ‘clear alternative’, just how clear must it be? Would a non-agreement agreement between Labour and the SNP constitute a sufficiently ‘clear alternative’?

Still, even if Cameron did cling on in these circumstances, and even in the absence of a ‘clear alternative’, he would lose the first relevant vote in the Commons, and would be out. And Miliband would be in. The crucial constitutional point is that the prime minister must be the person ‘who is best able to command the confidence of the House of Commons and should form the next government’. The position is straightforward: if that person isn’t Cameron, it’s Miliband. From the constitutional point of view, it doesn’t matter if Nicola Sturgeon is a baby-eating secessionist, as long as her party sides with Labour on confidence votes.

I think the talk of a prospective coup is too strong, but the right-wing press are making an each-way bet here. If the scaremongering helps the Tories, so much the better. More likely, it helps to set up a narrative in which a Labour minority government is not in possession of a genuine mandate. This is a theme they can run with for a looooong time. It makes you tired just thinking about it, the idea of just how hard they would flog this horse over the next five years. And it would be quite likely to be a full five years, too. One of the ironies of the coalition is that by passing the 2011 Fixed-Term Parliaments Act, they have made it easier for a minority government of the opposite political hue to battle through for a full term. Under the old system, a government fell if it lost votes on ‘confidence and supply’, i.e. formal votes of confidence or votes on crucial government business. After the new act, a government only loses power if it loses a formal vote of confidence. That’s a much higher bar: to bring Miliband down, the SNP would have to join with the Tories. North of the border, that would not be considered a good look. Sturgeon’s promise to ‘lock David Cameron out of Downing Street’ would sit oddly with helping the Tories back into office via a confidence vote. The coalition’s electoral law has made life easier for its successor.

In the meantime, the Tories and their allies in the press are going to hit this one pretty hard. Remember the long-term economic plan? We’re about to have 48 hours of short-term political panic.