The top half of the front cover of the Daily Mail today is of course trivial: the big story of the meeting between Theresa May and Nicola Sturgeon is, obviously, the plummeting relations between Westminster and Holyrood and whether we will still have a United Kingdom in five years’ time. The big story is not the quality of two middle-aged women's legs. But it is also really rather brilliant in how it has worked as a bait for the Left – which by reacting in an absurdly overblown way has merely revealed its own obsession with trivia.

In a country where millions are struggling to afford a decent home, where cases of slavery still emerge, where the government has just brought in a tax cut for people inheriting million pound homes while simultaneously trying to jack up taxes for tradesmen on modest earnings, you would think there was ample for the Left to get its teeth into. But no, the only issue on which it seems able to stir itself into a state of high passion any more is its disgust for the Daily Mail.

Owen Jones’ reaction in the Guardian is on the verge of self-parody. 'The bigots are winning the battle for the country’s future and that should terrify us all,' he writes. Er, over a picture of a pair of legs? Alastair Campbell reacts by declaring the Daily Mail ‘utter scum’ and called for everyone who sees a copy of today’s Mail to rip it in half. Yes, this from a man who a week ago tweeted that Martin McGuinness was a ‘great guy’. Presumably, if Paul Dacre sent his hacks out kneecapping people rather than merely shooting their legs in a photographic sense his opinion of the Mail would improve at least to one of grudging respect.

The Mail front page has even brought Ed Miliband out from retirement, as well as incurring the wrath of Yvette Cooper, John Prescott and the thousands who have taken the matter to the top of the Twitter discussion board. Doesn’t it worry these people that they can only seem to generate a national debate while they are bashing the Mail?

I have an interest to declare as a Mail contributor, and of course my view of the story might well be influenced by flattery that the newspaper for which I write can have become so central to Britain’s cultural life that among many on the Left it transcends all other issues. But I know how this row will play out in the greater mass of the British population: utter bemusement that a bunch of overgrown student politicians can get themselves so worked up over a caption which tried to introduce a little levity into a rather grim meeting between the two most powerful women in Britain.

If the Left wonders why, for the moment, it has become incapable of winning elections in Britain, it should reflect on how far its obsessions have drifted from the concerns of millions of ordinary people.