It’s not just who our pop heroes are that marks the passing of the generations; it’s how those heroes present themselves. Kevin Rowland, who turns 70 next week, appeared on stage for his London album launch in a jaunty sailor’s hat and striped top, looking as though he’d just come from a fashion shoot. Mac DeMarco, aged 33, ambled on in baseball cap, shlubby T-shirt and jeans. Rowland was upstanding, commanding and just a little forbidding. DeMarco sat on a stool and told a long story claiming that he and his keyboard player had been Oregon miners: a story which extended to include coprophagia, hair fetishism and maple syrup. Rowland is total commitment; DeMarco is total detachment.

Both were adored above and beyond the usual level of dedication. Rowland’s crowd was heavy on men of a certain age who are fond of headgear. DeMarco’s was much younger, and dressed like him. But at both shows there was the sense of being among people who were watching not just a singer, but a teller of elemental truths. Which, as a man well into middle age, I found troubling when what I was hearing about was coprophagia, hair fetishism and maple syrup.

In truth, I’ve felt a little wary of DeMarco since 2015, when as an editor I sent a young woman writer to interview him, and he conducted the whole thing in his underpants. When she returned to the office, the word ‘creepy’ was used. For the record, I am not accusing him of anything other than not understanding the importance of trousers in the workplace, but I do think trousers very much have their place in the interview setting.

DeMarco’s generational appeal appears to be based on the dichotomy between his nothing-really-matters persona – claiming his failures for himself, as virtues – and the surprisingly heartfelt sweetness of many of his songs. He’s both disguising and presenting his vulnerability.

That said, it took a good hour to get to that stuff – the show opened with his recent instrumental album Five Easy Hot Dogs played in full, with his three-piece backing band. Which was, well, fine. Each of the 14 tracks had the same lazy lope, like fragmentary instrumental demos for some long-forgotten Beach Boys album.

His very tone contributes to the sense of distance – his guitar, both on record and live, sounds drunken, as if the notes somehow bend being plucked and emerging from the amps. So even when he’s singing a song as simply heartbroken as the oddly titled ‘20191012 Fooled By Love’ – ‘Why am I still crying?/ There’s no use left in crying/ But I’m still out here crying/ When I’ve been fooled by love before’ – he leaves the listener with the faint suspicion that he doesn’t mean it. It’s an odd feeling, like talking to someone you suspect of playing an elaborate practical joke in their unpredictable unearnestness.

Kevin Rowland would hate you to think he was playing any kind of joke on you. Everything he does is sincere: so sincere you want to shout out that it’s OK to relax. You might sum up the entire Dexys’ worldview with a line from an old song on Too-Rye-Ay: ‘I’m going to punish my body… until I believe in my soul.’ Quite how he would project that when all he was doing, more or less, was singing over a backing track (the Midnight Runners, for this show, consisted of one man with a laptop and a keyboard) was a moot point, but project he did.

Rowland attracts a fierce devotion, particularly from men who seem to see him as an exemplar of self-flagellating honesty. (I think he’s analogous to Bruce Springsteen: neither is a conventionally good singer, but both articulate something – often through sheer force of personality – that rings out deeply in their audience.) So everyone listened respectfully to the songs from the new Dexys album, The Feminine Divine, but it was when we got to a medley of ‘Soon’, ‘Plan B’ and ‘I’ll Show You Now’ from 40 years ago, that everyone started really feeling. ‘No need for pain, nothing physical, no violence/ Just intense thought, some space, some silence/ Just something pure and precious worth having, soon I won’t care,’ Rowland sang, from a tiny stage, to a couple of hundred people, and it was as if the world stopped turning for a few minutes. The middle-aged men briefly started to sing along, then realised it was best left to Kev.

And, yes, it would have been nice to see a horn section, a string section, a drummer, a bassist, guitarists and Helen O’Hara playing violin. But as long as you have Kevin Rowland and his astonishing voice and his complete obsession with being Kevin Rowland, you’ve got Dexys. He can’t help being magnificent.