I was musing aloud about Nicola Sturgeon when the story first broke claiming that she had described to the French ambassador a preference for David Cameron as prime minister. The speed and force of Sturgeon’s own denial was such that I thought it a shame not to have at least solicited a quote from her to stick at the end of the original allegation: you know, for balance. I was musing on Twitter, in fact, so I don’t know if you could call that “aloud” so much as “yelling at the top of my voice”.

Anyway, soon enough, the French consul general denied it. “Let’s just wait and see what the ambassador says,” came the suave replies. Yup. She says it never happened. “And diplomats always tell the truth, and never strategically deny anything?” Well, OK ... but if we need to treat the denial with suspicion, why didn’t we approach the original charge with a bit more scepticism? “Let’s just have a look at the memo …”

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Right. The leaked memo, first published by the Daily Telegraph, is a third-hand account from a civil servant, who has doubts about whether the comments were ever uttered, wondering at the end if something was “lost in translation”. Yet on they came, the waves of certainty: it must be true because it had “the ring of truth”: because “I’ve sat in these meetings for decades”; because it would be understandable for Sturgeon to become “loose-lipped” in front of a sophisticated diplomat (some elusive nastiness in both the phrasing and the idea: she’d been undone because she’d put herself among people with whom she didn’t belong).

Steadily, the assertion solidified. Since a David Cameron government would clearly bring Scotland closer to independence, and since that was Sturgeon’s highest goal, it started not to matter whether or not Sturgeon had said it at all. She plainly thought it.

Yet it did matter. It’s too early in the electoral process, surely, to start putting politicians on trial for their thoughts. I didn’t even care that much whether it was true, I just wanted a scrap more evidence. The confidence of Twitter turned to scorn: I obviously didn’t know how newspapers worked, or how the Foreign Office worked, or how a meeting worked, or how the truth worked. Lucky me, with my high standards and my superiority complex. By Saturday morning, Ed Miliband was on the BBC, castigating Sturgeon for the “revelation”, when it was increasingly unclear that anything real had been revealed.

Something is lost, when credulity pushes past reality into believing any damned thing you want to believe. Some courtesy is lost in the tenor of the debate; arguments get nastier in inverse proportion to their solidity. Politics suffers as a whole, when you push back the curtain and see nothing but bare assertions and empty confidence.

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Yet none of it mattered over-much to the subject of the allegation, who has used it to force open Labour’s position: will they, Sturgeon asked in the Observer, join forces to keep the Conservatives out of power? If they hate austerity so much, will they throw their weight together with that of the SNP, who hate it too? As an approach, it is so deft – exposing the contradictions of the Labour party between the ideals they claim to uphold and the enemies and rivals they fixate upon – that one, almost reflexively, picks it over for signs of politicking, admires it for a checkmate.

But what if she’s not trying to maximise her advantage? What if she’s not out to embarrass Miliband? What if she’s actually on the level? What if she is genuinely worried about the entire nation, not just the bits in her purview? What if she’s trying to build a real alliance, based on a shared belief in social justice and humanity’s innate generosity? Then Westminster is really in trouble. Never mind being finessed over the Barnett formula or trounced in Dundee: that kind of politics, the party machines were built to understand. Can any of them adapt to a genuine spirit of cooperation, in which considerations of the individual ego, and that of the party, are put aside? It is unimaginable.

To accept Sturgeon’s offer, Miliband would have to say, publicly, that he didn’t care about losing Labour’s seats to the SNP on 7 May: it is a near certainty that he’ll lose them anyway. Everybody knows it, nobody disputes it. Yet in a political climate of “winner” and “loser”, where Miliband has to make a mental note to himself to approach a debate like a “happy warrior”, the combatants themselves are allowed to give no honest appraisal, no sign of even knowing what the reality is. It is the most preposterous thing, the way they parade their wives around and put their babies in dispatch boxes, all to seem more “human”; the one human trait that would make them seem real – self-awareness – is utterly forbidden.

To enter a pact with Sturgeon, Miliband would have to accept Scotland as, if not an equal partner, then at least punching above its weight. He would have to let go of old hierarchies in favour of a new politics in which he might no longer look like a leader. He never has, of course, but that’s another one of those things he’s not allowed to admit.

The cost of all this would be enormous, and for what? The end of austerity. An end to the redistribution of money from the bottom and the middle to the top. The pursuit of a new kind of social democracy. Who even knows whether that’s what Labour want? It’s not on any of their mugs.