In the private dining room of a central London hotel, Ed Sheeran is telling me about the time he smashed Justin Bieber in the face with a golf club. “We were in Japan. We’d been out to a dive bar. He just drank water and I got hammered. Then we went to a golf course, and he lay on the floor and put a golf ball in his mouth and told me to hit it out of his mouth. I was like, ‘Fuck, I need to aim this properly,’ and I swung. And you know in films when someone gets punched, and you hear that fake sound, like a slap? But in real life when someone gets punched, you hear that dull thud, a bit sickening? I heard a sound like the last one, and saw his security guard looking at me like” – he pulls a horrified expression. “I’d cracked Justin Bieber right in the cheek with a golf club. That was,” he concludes, “one of those ‘What the fuck?’ moments.”

Ed Sheeran: ÷ review – everybloke charm fails to mask Divide's calculating soul Read more

Sheeran looks pretty much the same as he did the last time I interviewed him, backstage at the Brixton Academy five years ago, although I get the feeling his glasses might be a little more upscale, the baggy skatewear slightly more stylish and expensive. Frankly, you would hope so. Then, he was a 20-year-old singer-songwriter who had unexpectedly sold 1m copies of his debut album, +. Today, he is the biggest male pop star in the world. Not long after those Brixton gigs – and in part thanks to the patronage of Taylor Swift – he broke America. The rest is just mind-boggling statistics: 24 hours after it was released, his recent single Shape Of You had been streamed 6,868,642 times on Spotify alone; within a week, it had been streamed 53m times. He is too polite to say so himself, but the charts are filled not just with his records – at the time of writing, he occupies three out of the top four places in the singles chart – but with records that sound like him. The records that sound like him frequently do so because he wrote them: he has penned songs for everyone from Robbie Williams to the Weeknd. The question isn’t really whether Sheeran’s third album, ÷, is going to be a hit, so much as whether its sales figures are going to rival those of Adele’s record-breaking 25.

If he looks the same, his manner seems slightly different. He is still affable, self-deprecating, funny – as nice and down-to-earth a multi-platinum global star who has smashed Justin Bieber in the face with a golf club as you could wish to meet – albeit slightly more guarded and concerned about how things will look in print: more than once, he interrupts himself with a plaintive: “Do I sound like a cunt?”

“I try to be as honest as possible,” he says, “because I think the moment you’re media-trained and hold back things, you become one of them, but it’s getting harder because … every time I give an interview, there’s three news stories about what I’ve said in it the next day.”

But aside from that, there is something else – a steely confidence and ambition about his music and career that either wasn’t there or I failed to notice last time around. He is blithely unbothered by hanging out with other musicians who have said they don’t like what he does – “I know Noel Gallagher doesn’t like my music, but I get on with him as a person, so why does it fucking matter?” – and professes to no longer care what critics think about him. “I was self-conscious about it on my first album, because I’d never had any success, I’d never sold any records, never sold a ticket, and I was terrified that it would be over in an instant. The album got panned by the critics and I was like: ‘Fuck, this is it.’ But now I’m at a point where, even if I get a one-star review for every album I release for the rest of my life, I’ll still be able to play music.”

He talks about how 2017 is going to be his year, how happy and settled he is with his girlfriend, Cherry Seaborn, an old school friend; how all the artists he sees as competition – “Adele, Beyoncé, Taylor, Drake, the Weeknd, Bruno” – have already put albums out, so ÷ has “kind of a clear lane”. When I ask how he would feel if it did well, but sold less than its predecessor, 2014’s 14m-shifting x, he says: “I’ll bet you anything now it won’t. I don’t think there’s any possibility it will. The next album, I promise you, will sell less, but this album will sell more. I don’t think I’ll have a year like this again.”

Facebook Twitter Pinterest Sheeran on stage at Wembley Stadium in 2015.

Photograph: Christie Goodwin/Redferns via Getty Images

In fact, he says, he’s less interested in how it sells than ÷ being “something like Damien Rice’s O, that in my lifetime is one of the most important records for me. I’d love for some kid who in 20 years’ time is a huge artist to be like, ‘Wow, that album.’” He’s proud of its contents, of the work he put in to ensure it’s “the biggest fucking pop album it could be”. It took him at least three goes to get it right, he says: hundreds of songs written, hundreds discarded or handed over to other artists. One of the ones he let go was a jokey thing he’d written with Rihanna in mind, with the hook: “If you like the way you look so much, you should go and fuck yourself.” With the lyric suitably cleaned up, it went to Justin Bieber and became Love Yourself – globally, the biggest-selling single of 2016. He wrote so many songs he started forgetting he’d written them: when the producer Diplo contacted him, asking if Major Lazer could use a track called Cold Water that his co-author, Benny Blanco, had passed his way, he had no recollection of writing it. It went to No 1 in 17 countries. On the other hand, he doggedly fought his record company to include a track called Galway Girl, which seems faintly telling. Most artists wouldn’t get in a pitched battle with their label over something wildly uncommercial, but Sheeran ended up locking horns with his over a bodhrán and fiddle-bedecked jig that one suspects is going to blare out of Irish theme pubs for eternity. It reminds me of something the marketing manager at his record label told me five years ago, about how his constantly talking to journalists about winsome acoustic duo Nizlopi – or, as she put it, “bloody Nizlopi” – had left her “tearing [her] hair out”: “They’re not a band that I would exalt as particularly cool, but then I’m not Ed … He’s not cool. Well, he’s cool in that he’s a cool guy, but he’s not, like, a wannabe hipster. He doesn’t give a shit.”

Sheeran says of his label: “They were really, really against Galway Girl, because apparently folk music isn’t cool. But there’s 400m people in the world that say they’re Irish, even if they’re not Irish. You meet them in America all the time: ‘I’m a quarter Irish and I’m from Donegal.’ And those type of people are going to fucking love it. My argument was always: well, the Corrs sold 20m records. The label would say, ‘Oh the Corrs, that was years ago,’ but who’s tried it since the Corrs? There’s a huge gap in the market, and I promise you that in two years’ time there will be a big folk band that comes up that’s pop, and that will happen as a result of labels being like: ‘Oh shit, if he can put a fiddle and uilleann pipe on it, then we can try it as well.’”

Galway Girl aside, perhaps the most striking track on ÷ is its opener, Eraser, a hip-hop influenced track that, among other things, suggests “money is the root of all evil and fame is hell”. It feels odd coming from Sheeran, who seems to have been navigating the choppy waters of global celebrity with enviable ease. There has been no drink- or drug-assisted crash, no public meltdown, no scandal, no former friends or partners selling lurid stories to the tabloids, just a speedy but steady ascent into pop’s upper echelons, his famous affability securing him a plethora of celebrity friends.

Apparently, though, adjusting to success hasn’t been as straightforward as it might appear. He is, he says, “having a fucking great time” for 90% of the time, but the other 10% he “can kind of wake up and think: I had so much more fun when I was broke, sofa-surfing. I felt like more of an artist.” Part of the issue is money: according to Forbes, he earned $33m (£26.78m) last year alone. It is, he says, a distinct improvement on the pre-fame days when he was reduced to sleeping rough after gigs – “I don’t have that worry in my mind any more, when it’s 11 o’clock at the venue and you’ve made no money and you have to get a train home, but you have no money for the train home and you have nowhere to stay” – and on one level, he seems to be enjoying the fruits of his success in fine style: “I did what any bloke would do – sorted my family out, bought a sports car that I never drive because I look like a tit in it, bought a house and built a pub in my garden. I spoke to every dude I know and I was like, ‘What would you do in the same position?’ and they went ‘Build a pub.’” On the other hand, he seems faintly troubled by his wealth.

“Money’s such a weird thing. The way it changes certain people around you, the attitude they have towards you, and it changes the people you think it wouldn’t change. Just small things. I remember being in a club with a couple of friends that I was close to, we ran up this hefty bar bill – it was 700 quid or something – and I sorted it at the end of the night, then left. I got a call the next morning from the bar: ‘Oh, your mates came back later and they ran up another 600-quid bill and they just said to charge it to you.’” He sighs. “I know that’s a proper first-world problem, but … you just see people you’re close to seeing you as a cash machine rather than a mate, like if they hang around you they’ll get stuff from you. Whereas my mates back in Suffolk, as soon as we get to the pub they’ll buy me a drink. Small things like that, rather than going out at the end of the night and kind of sneaking off.”

I was on easyJet on my own, no security, with all the pissed Benidorm lot. Horrendous. The worst experience of my life

There are other issues. A couple of years ago, thanks to a slightly convoluted set of circumstances involving cutting short a holiday with friends in order to shoot a scene in The Bastard Executioner, a historical drama he had a guest role in, he ended up taking a flight from Benidorm to London “on my own, no friends, no security, at two in the morning, on easyJet, with all the pissed Benidorm lot. Couldn’t even wear a hat or a hood because it was so fucking hot, so I was just out there in the open.”

You could imagine this proving to be a trying two hours, but it genuinely seems to have permanently traumatised him. “Horrendous. The worst experience of my life. Like so bad, that I started getting panic attacks. I’ve never had anxiety in my life, it’s been something I read about in interviews with other artists and thought, ‘Thank fuck I don’t have that.’ It’s just something that happened quite recently. I get really claustrophobic. Like, there’s no way I could do this interview out there” – he jerks his thumb towards the door, on the other side of which lurks the hotel lobby – “I just don’t like groups of people that I don’t know any more, I can’t do crowds any more. I can go to a pub, but only if it’s a pub that no one would go to. So me and Cherry go to a pub near where I live for Sunday lunch, we get a little corner table out of the way, and that’s fine. I can do that, but standing in a pub, no, I couldn’t do that. Couldn’t do it.”

Around the time of his 2015 Wembley Stadium gigs – he was the first artist ever to play the venue completely solo, just him and his guitar and his loop pedal onstage – he was “really going up the wall”, as he puts it. “All of those things that when you get into the industry people say ‘Be careful of this, be careful of that,’ I was doing all of them.” At one point he found himself crying in front of, improbably enough, the David Brent film: “When he was paying his band to hang out with them, it was like, ‘Shit, I’ve definitely been in that situation.’” So he unplugged himself from social media and went travelling for a year: Iceland, Ghana, Japan, a visit to Liberia for Comic Relief. He talks about how much he loved it: the anonymity, being away from selfie culture, “where everyone’s trying to show people how amazing their life is”. Does he think he could walk away permanently? “Not from music, but I could walk away from being this massive, so long as I controlled it. I’m not continually going to have this ambition. I know I’m not always going to maintain it. I’ve played Wembley Stadium three nights in a row and if I end my career doing one night at Shepherd’s Bush, it’s fine, because I’ve achieved it. I’ve won the awards you’re meant to win, sold the records you’re meant to sell. I never did it for money, and I don’t really need any more money. At the end of the day, I make music to make music and as long as I can keep doing that for the rest of my life, it doesn’t really matter. I was talking to Taylor about this, actually: the moment we see it fading, it’s like, ‘Right, time to have kids!’ It’s fun now, in my 20s, but there’s more to life than selling millions of records.”

He laughs. “Actually, I don’t know. When it starts fading, it might completely destroy me. We should do an interview when that happens.” And then he signs some autographs for my kids, offers a manly hug goodbye, and heads out for a meal with Russell Crowe: “I’m taking Gladiator out to dinner! How cool is that?” That’s the other bad side-effect of fame, he says. It’s turned him into a terrible name-dropper. “But I’m a kid from Suffolk, not that attractive, literally grew up in the middle of nowhere, who now has the opportunity to move in a Hollywood world where people I’ve grown up watching want to hang out with me, and I’m really fucking excited by that,” he shrugs. “I don’t care what people think. They’d do exactly the same thing in my situation.”

• ÷ is released on Atlantic on 3 March.