Lewis Capaldi wants to make very clear how this is going to go down. “I’m going to sing some songs, you’re going to listen to them, and then we’re all going to fuck off,” says the Scottish singer-songwriter, swigging from a can of lager. Those songs, he adds, will all be sad, if not actively depressing. After he’s done, he intends to get “steaming”. The audience loudly endorses this plan.

It has long been the case that American artists tend to valorise hard work and gruelling professionalism while their British counterparts prefer to appear as if they’re making it up as they go along. Even so, from the title of his 2019 debut album, Divinely Uninspired to a Hellish Extent , to a profoundly dishevelled anti-style that makes Ed Sheeran look like Cary Grant, Capaldi takes self-deprecation to extraordinary lengths. He gives the impression that he rolled out of bed one morning and, to his great surprise, somehow fell on to the top of the charts. Behind the scenes, of course, that is not quite how it works ? his sturdy, stirring songs were crafted with the aid of a fleet of co-writers and producers ? but Capaldi’s impersonation of an accidental pop star isn’t exactly disingenuous. It feels, in part, like a coping mechanism. His album has been No 1 for six weeks, his ballad Someone You Loved topped the charts for seven; his shows sell out in record time, and he’s still only 22.

A fishmonger’s son from Bathgate, Capaldi spoke recently about belonging to a generation that has seen countless stars rise and fall and knows every pothole in the road. So what better way to manage such a dizzying ascent than to treat the whole experience, on some level, as if it were an absurd trick of fate?

A few hours earlier he revealed more of himself during an intimate warm-up show in Trinity Apse, just off Edinburgh’s Royal Mile, in front of no more than 50 people: three stripped-down songs followed by an interview with the comedian Daniel Sloss . Up close it’s apparent that Capaldi served his apprenticeship performing cover versions in pubs, wrestling noisy, boozy rooms into submission with his burly, husky voice and quick wit. It’s no discredit to the songs to say that the interview is even more entertaining.

Sloss calls Capaldi “the man that every comedian in Scotland hates because he’s funnier than all of us”, and you can easily imagine him delighting the Edinburgh fringe with a standup show about going platinum by mistake. Uproarious anecdotes about feuding with Noel Gallagher and lunching with Elton John are interspersed with increasingly surreal and obscene flights of fancy, all underpinned by the suggestion ? not entirely flippant ? that his spectacular good fortune is about to come off the rails any day now. “The backlash is coming soon,” he promises.

In West Princes Street Gardens , a picturesque natural bowl in the shadow of Edinburgh Castle, Capaldi delights in deconstructing the rituals of the pop concert. He flatters the crowd with a standard line ? “So far you’re better than last night” ? before adding: “But we’ve got a lot of songs left and you could still fuck this up, so don’t get cocky.” His band members, all of whom are dressed in pillar-box red, are introduced by Capaldi impersonating the style of a solicitous gameshow host: “What’s your name and where do you come from?” The last song, he says, is obviously not really the last song, and he’ll be back for an encore, but first he’s “going to take a pish”.

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It’s not unprecedented to see an artist offer an ironic running commentary on his own gig, but it does become notable when said artist is the biggest new act in the country and sings about nothing but romantic calamity. Like Adele before him, Capaldi’s throaty, blue-eyed soul draws its power and specificity from a formative breakup, which he anatomises with a masochistic thoroughness. Sparser songs such as his 2017 debut single Bruises wallow in damage and loss, as if reluctant to move on: “I hope I never lose the bruises that you left behind.” Even the relatively thumping Hollywood , which he says you can dance to as long as it’s “with tears in your eyes”, is about his failure to distract himself from what he’s messed up.

This emotional monomania is enlivened by distinctly Scottish references to Buckfast and the Edinburgh pub 99 Hanover Street (which happens to be just five minutes’ walk from the stage), and by some clever phrasing. The informality of “I was getting kinda used to being someone you loved ” could read as either fatal hesitancy or fatal complacency. Still, it would be good to hear Capaldi explore different emotional states, inject more of his between-song wit and joy into his songwriting, and thus pull his impressive voice in new directions. There’s more to life than girl dumps boy.

For now, he pulls off the impressive feat of making a raucous, celebratory show out of undiluted misery. He lets the austere, self-flagellating Lost on You and Headspace unfold without leavening the intensity with a gag, but the rest of the time he seems to be trying to outwit his own lyrics and jostle the pain out of them. Surely hearing 6,000 people, mostly women, sing back every word to him must help. There is an ecstatic sense of homecoming to this show: a freshly minted Scottish superstar performing a lap of honour in the heart of the capital in the middle of festival season.

While the show is judiciously spiced with eruptions of confetti and showers of pyrotechnics, Capaldi claims his budget doesn’t stretch to fireworks. Instead, he explains towards the end, he plans to piggyback the amply funded efforts of the military tattoo up the hill, if only he can get the timing right. To this end he inserts a solo cover version of Paolo Nutini’s Last Request , one of the songs he used to wow the pubs with not so long ago, into the encore. It works perfectly.

Just as the crowd is singing the chorus of Someone You Loved , over and over again, the sky explodes with colour. Only when he leaves the stage does the rain, long threatened, finally fall. Thus the night closes with a tingle of serendipity. Much though Capaldi likes to imply that his success is unexpected, perhaps even undeserved, things so far have a habit of working out for him.