Normally when I’m irritated by the Mail, it comes down to professional envy. They are the most formidably commercially successful journalistic enterprise in Britain today, and whatever one thinks of their politics this provides them with resources to do some really impressive stuff. So much of the criticism routinely directed at them is predictable and defeatist, the sour grapes of those on the other side of the ideological divide who wish they could communicate their ideas even half as effectively. Sometimes, though, there are days when they go too far. Sometimes they print things so myopic that you feel a fly on the wall might learn something genuinely new about human nature.

Today is a case in point. What are they thinking? It was grim and predictable enough to run a hit piece on Ed Miliband’s father with the headline ‘THE MAN WHO HATED BRITAIN’ at the weekend, even if the article itself was a relatively modest piece of biography that couldn’t begin to justify so inflammatory a headline about a Jewish refugee who served with the Royal Navy during the war. If more of the people who hate Britain expressed it that way, you might think, we would all be an awful lot safer.

This morning's follow-up didn’t just make things nastier – it stoked the flames. The paper agreed to run a moving piece by Ed Miliband defending his father against this unpleasant slur. When I heard that last night I immediately thought, good on the Mail – it takes a grown-up publication to admit when it’s gone too far. Except that as it turns out the Mail hasn’t quite done that. Instead, it has run the Miliband piece as part of a double page spread, alongside an abridged version of the same article it ran just a few days ago and a leader with the forceful headline: ‘An evil legacy and why we won’t apologise’.

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It trivialises Miliband Jr’s justifiable anger as a ‘strop’ and mocks him for ‘stamping his feet’ and being ‘tetchy and menacing’, as if the Mail doesn’t have its own well-worn line in questionable outrage. It suggests that ‘Red Ed’ invited this treatment by daring to tell people about his father’s escape from Nazi persecution. It finds something repellent in the idea that you might be motivated more by the fight against the Nazis than the fight for Britain, by which astonishing logic the Second World War and the invasion of Iraq were morally equivalent conflicts. (Anyone who wouldn’t rather fight against the Nazis than for Britain is, I would suggest, not someone who should ever be allowed near a gun.) It talks about ‘degenerates’ and ‘useful idiots’. And, after 1,000 words of this sort of stuff, it builds to a towering crescendo, which links press reform (of all Red Ed’s alleged offences, to pick that one!) to Marxism and warns that if this immigrant’s son is allowed to do what he wants he will “have driven a hammer and sickle through the heart of the nation so many of us genuinely love”.

God knows how you ‘drive’ a sickle through anything more substantial than a piece of cheese, but forget the dodgy phrasemaking and focus on the unpleasant insinuations. Sometimes people write the Mail off as a sheerly cynical exercise by people who know better, but this isn’t that. That it is heartfelt only makes it more troubling.

As the Mail editorial was being published, the American government was being shut down, a quite extraordinary state of affairs for a superpower. That came about because US politics has retreated even more than our own from a real discussion of substantive issues to point scoring and tribalism. There is a line, it seems to me, from Sarah Palin calling Barack Obama ‘un-American’ to Republicans in the House feeling entitled to hold the country to ransom so they can refight a political battle over healthcare that they’ve already lost. The connection is this: it’s not that you think the other side are wrong. It’s that you think they aren’t entitled to a view.

We are, I’m glad to say, still a long way from that over here. But there’s certainly more of it about. And when our most influential newspaper starts chucking around claims that people who they disagree with ‘hate Britain’ instead of ‘have stupid ideas’, we take another small step down that road. No apology will ever materialize, of course. But if cooler heads don’t prevail even after something like this, one wonders what on earth it would take.