Nearly five years ago, I saw One Direction live. Twice, on consecutive nights – on the first two dates of their On the Road Again world tour. Once was for work, to review the show. The other was for the sheer, heady, sugar-rush pleasure.

I was, I’ll admit, a little on the old side for a Directioner, even then. Most of the 45,000-odd crowd was much younger – not that that you would necessarily be able to tell from the saucy suggestions on their homemade signs. “I don’t want to draw attention to them,” Liam Payne had said fussily on stage.

It was an on-brand comment for the then-21-year-old Payne, who, had the harried, slightly anxious energy of a father-of-four at Disneyland. And no wonder: it was clear, even to me, that Zayn Malik had checked out, barely bothering to conceal his rolling eyes. He would be gone within the month, marking the beginning of the end (or “indefinite hiatus”) for the biggest boy band in the world.

“It was a point where every day, you didn’t know whether it was going to be the end,” says Payne, sitting in the offices of his PR company in central London. “It was so touch and go, at every single show. I was slowly losing the plot.”

Now 26 and almost totally tattooed, Payne has a new album on which he raps about getting rowdy on Bacardi and being “free” from 1D. At the same time his very-nearly-naked form is plastered on buses and train stations in a provocative ad campaign for Hugo Boss.

Yet Payne is as polite and agreeable as if he were talking to his best friend’s mother. He is tired he says after an energetic early morning music video shoot. “There was a trampoline involved,” he says, sucking on his silver Juul. “It was hell – but it will look great.”

Gym beast and sex symbol are relatively new tags. His role as the diplomat of the group was established from the time they were first assembled from five solo applicants on The X Factor in 2010.

Payne auditioned when he was just 14, but was told by Simon Cowell to “come back in two years”. He did – and, eyes serious beneath his enormous fringe, blew the judges away with a brassy rendition of Cry Me a River.

Growing up in Wolverhampton, he had been a talented cross-country runner. But a fan of Usher, Justin Timberlake and Chris Brown, he was drawn to singing as “the thing that made my parents proudest”. His backup plan, had he not got through on X Factor, was to follow his father into an aircraft fitting factory.

Once grouped in One Direction it took the five boys, then between 16 and 19, to pull together. “At the start we couldn’t get past our own egos,” says Payne. There would be fights over who got to sing what part, and even personal style. “Everybody had their own little thing – it was like having four older brothers.”

Payne went on to write songs for the group, contributing to two-thirds of their 2014 album Four (arguably their best) and even earning a production credit on 2015’s Made in the AM. But in the early days he would be the one to sing the opening part because, he was told at the time, he “used to settle everybody”.

Louis Tomlinson, Harry Styles, Niall Horan, Liam Payne and Zayn Malik in 2012. Photograph: Fox/Getty Images

Payne says he was a more experienced performer than the other boys, and a “bit more mature” – which he puts down to spending more time with his dad than his peers, and being so focused on a career in showbusiness. “I’d lived a different lifestyle from 14 to 16. Most kids try alcohol and experiment – I never did any of that because I thought there’s a chance that I might make it.”

Management took advantage of this, he says, telling him his “very specific role” in the group was to keep the rest in line. “I was like, that’s great, innit – because then everyone in the band thinks I’m a dick.” He remembers one of the band’s first hotel stays. “We’ve got plates being thrown out the window, mattresses being ridden down the stairs, and I’m getting calls from the manager saying: ‘You need to sort it out’.”

It wasn’t lost on the fans. Where Malik and Styles were the heartthrobs, Payne says he was classed as Mr Boring. “When you’re at the stadium, and if you get the least screams, it’s like: ‘For fuck’s sake.’”

After a year playing 1D-Dad he gave up and learned to have fun. “If you can’t beat them, join them” – at which point, he notes wryly, the band’s public image became more cheeky and carefree. “And the more fun we had, the more successful it got.”

He recalls performing to sold-out stadiums night after night, seeing “hundreds” of iPhones being thrown onstage in the vain hopes of their being returned with a selfie. “It’s like the kids just lost their minds.”

“There were parts of it that were a bit shit, like there is with anything,” he says, “and there were parts of it that was just euphoria.”

He recalls seeing 15,000 fans camped outside his hotel room in Lima, Peru. Security had advised them to stay inside all day, and because “they were the adults, we thought they were in charge. Then over time we started to figure out that they weren’t, and that’s when we used to run off.”

Yet the adrenaline peaks of performing, followed by long troughs of tedium, were akin to a drug addiction, says Payne. He turned to alcohol. “Doing a show to however many thousands of people, then being stuck by yourself in a country where you can’t go out anywhere – what else are you going to do? The minibar is always there. ”

One Direction. Photograph: PictureGroup/REX

For a time, he was also taking an epilepsy drug as a mood stabiliser that he says affected his cognitive functioning under certain lights. Payne says he had been well advised to take it, to counter the “erratic highs and lows” he was experiencing – “I just needed a little bit of help to keep me stable” – “but under certain lights on stage or during interviews, I wouldn’t be able to tell them my name”.

The day we meet, Payne has made headlines for telling Ant Middleton on the pair’s Sky One show that the loneliness of fame had “almost nearly killed” him. When Middleton asked Payne if he had ever wanted to act on those feelings, Payne said that he had: “100%”.

He is not inclined to discuss this today, “because it’s a bit dark,” he says, a touch brusquely – “but yeah, it was very touch and go at times”. This was both in 1D and afterwards, he clarifies. As One Direction got bigger and bigger, he says, “I was like: ‘I don’t really know how to deal with this’. Once you start, you can’t really press the stop button.”

The “indefinite hiatus” button, though, was easier – in mid-2015, four months after Malik’s departure, the band made the decision together. “It was a little bit dark and twisted towards the end of it,” says Payne, “but the last few shows were really beautiful moments because the pressure cooker had been let off.

“It was almost like counting down to holiday – we were going to wake up that Monday morning with no schedule.” Afterwards Payne was in therapy for two years, and took six months off. “It was difficult at the start, because I didn’t really know anything about myself. It was a bit of a numb feeling.”

In early 2016, he started dating Cheryl Cole, 10 years his senior, and one of the X Factor judges to be wowed by his audition. He is vague about whether he thought coverage of the age gap in their relationship was sexist (“For me it’s like, you love who you love”), though he notes that the online rumour mill is now trying to claim his new girlfriend – 19-year-old model Maya Henry, whose face in close-up is his iPhone wallpaper – is younger than she is.

His son with Cole, Bear, will turn three in March. Payne had always wanted to be a young dad, but says he struggled at first. “I built it up so much in my head. Finding your feet in that relationship between child and father – it’s difficult.”

He contributed by cooking. “Cheryl was always really glued to Bear, so for me, I was like: ‘What’s my role in this? If I cook and look after her, then in turn I’m looking after him’ – that made sense to me.”

The couple publicly confirmed their split in July 2018, but continue to co-parent. Lately Payne’s schedule has taken him away for weeks at a time, which is “always difficult”, especially now Bear is old enough to notice. “But he’s good at using the phone and FaceTime.”

That schedule is about to get busier, with Payne’s debut album as a solo artist finally out this Friday. Laden with chart-friendly trop house, trap and Latin pop influences, LP 1 plays like a water cannon aimed at commercial radio – there is even a Christmas song.

It has been a long lead-up: the first single, Strip That Down, was released nearly two years ago and established Payne as the 1D member most influenced by contemporary hip-hop – perhaps too much so. A picture he posted to Instagram of himself in February 2018 wearing a chain necklace, flipping the bird and bragging about travelling by private jet was quietly deleted following ridicule.

Amid the success of Strip That Down, which was streamed over 1bn times, Payne was also still “struggling” with alcohol: “I just hid it very well.” He went on to spend an entire year sober – a necessary if boring step. “My social life completely plummeted. I always feel like you never get past the awkward first 10 minutes at a party, when everyone’s like: ‘Do we get up and dance, or do we just sit here?’ I don’t know whether it made me happier, but it was definitely needed.”

His more recent stint of self-discipline was to prepare for his nude photo shoot with model Stella Maxwell for Hugo Boss. In the lead-up, he was in the gym between “five and eight times a week, sometimes twice a day” and eating mostly chicken and vegetables – with no carbohydrates after 2pm and nothing at all after 8pm. For the last “stripping” phase, he ate nothing but porridge and white fish for a month. “It was horrible – but it definitely works.”

The shoot had been his idea, inspired by campaigns featuring David Beckham and Mark Wahlberg – Payne’s role models, whose cross-disciplinary celebrity shapes his own career goals. Last year he auditioned in front of Steven Spielberg for a part in next year’s West Side Story remake, and has been submitting audition tapes irregularly since. “It’s just trying to manage the time in between being a dad, a boyfriend, singer, model and whatever.”

Between the trap beats, tighty-whities and tattoos is he attempting to put across a new, more grown-up image? “Oh yeah, definitely.”

In One Direction, he was “Mr Vanilla – no one wanted to know a thing”. Then, with the “chain and rapper phase … I didn’t really know what I was aiming for, but it was actually exactly where we are right now. I just needed to find the right keys to make me feel like the man I wanted to be.”

Which is, he jokes, is “like a really English Magic Mike”. Do you like being objectified, I ask? “I think it’s quite funny,” says Payne, clearly delighted. The other day, he says, someone sent him a picture of an old lady walking past an enormous blown-up poster of him in his pants. Not bad for Mr Vanilla, I say. “Exactly.”

Liam Payne’s debut album LP1 is out on Friday 6 December.

• This article was amended on 7 January 2020 to remove a reference to Liam Payne “making the reserve list for the British Olympics team”.