A tangled expression crosses Josh Warrington’s gaunt face as he talks about holding his wife before he goes to war in the ring. “I always embrace her like I’m holding her for the last time,” the IBF world featherweight champion says as he remembers how, before he beat Lee Selby to win the title in May, they hugged even more intently.

“I always say: ‘I’ll see you after,’” Warrington explains, “and I kiss her goodbye. But it’s different now we’ve got kids [twin girls born a few weeks before the Selby fight]. I held Natasha much longer than normal because we were more emotional. Selby was such a big fight – we felt it. We’ve seen fighters get badly hurt and lose their lives. I’m not naive enough to think it won’t happen to me. So I always tell Natasha how I feel beforehand.”

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Warrington looks up when I say boxing is like no other sport. His face is cut and bruised from intense sparring in preparation for his title defence against Carl Frampton in Manchester next month. Warrington knows he will be tested like never before. “It’s a funny old game, getting punched in the head for a living,” he says before adding a more complicated sentence. “For some reason it’s addictive.”

The 28-year-old gazes at a deserted Elland Road. Warrington won his world title in front of a 20,000 crowd here, at the home of his beloved Leeds United, on a night when he surprised many by outboxing Selby. That spiteful contest offers a powerful conclusion to a new feature-length documentary about the Leeds fighter.

Fighting for a City, which follows Warrington over two years, is a compelling film. It’s beautifully shot and a reminder how raw drama, poignant vulnerability and riveting characters define boxing at its best. Warrington is at the heart of it, alongside his father and trainer, Sean O’Hagan, a rotund and heavily tattooed man who had no previous boxing background until he started working his son’s corner. O’Hagan is amusing, with a sharp tongue, but he was calm before and after his son’s stunning victory – and when talking to me for 30 minutes before this interview.

An excellent documentary, however, skirts some aspects of Warrington’s story – from his dad looking after him and his two brothers as a single parent to his past as a dental technician when the boxer was often tagged The Tooth Fairy. He would be making dentures by day while learning how to knock out teeth at night. Fighting for a City also does not fully probe the dangers faced by Warrington, and all boxers, in the ring.

There is still a powerful line in the film where Natasha Warrington, Josh’s wife, underlines the gravity of boxing. “He is willing to die in that ring,” she admits quietly.

Facebook Twitter Pinterest Josh Warrington’s twin daughters were born in the runup to the May fight, and he says he held his wife for longer than usual before the bout. Photograph: Christopher Thomond/Guardian

“Yeah,” Warrington recalls, “but there is one scene I didn’t let them capture in the film. It’s about [the danger of] losing my life and that last hug before Selby. We always stay in a hotel before a fight. At 6 o’clock on fight night she heads to the venue. I say goodbye and have an hour to myself, to reflect. When I leave the hotel, I go to war.”

Warrington suggests he does not feel fully alive between fights, as if he is in “a kind of coma” while waiting to step back into the ring. “I drift from day to day,” he says. “Don’t get me wrong. All this we’re doing now is very real for me. But, when it comes to fighting, I feel so alive. Obviously, when you’ve got kids, your outlook changes because this could be about me losing my life. But the fight’s always on my mind. I’ll wake up in the morning, and it’s the first thing I think of. I go to bed at night, and it’s the last thing I think of. Being successful in the ring brings bigger paydays and it can make a difference to their lives. I’ve got a plan I want to achieve as quickly as possible. And then be happy, be satisfied.”

He looks composed in the documentary as a turbulent two years end in the climax of a world title. But surely he felt differently on the inside? “Throughout the buildup I was relaxed. Even on the day of the fight I was nice and calm. But, when I said bye to Natasha, the nerves hit me. I thought: ‘What have I taken on here? What happens if I don’t win? How would I go down Elland Road again? How do I walk around the city centre? How would I be able to stay where I live, in Garforth, where there are signs to Selby?’ I’d see his name everywhere.

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“But as soon as I stepped into Elland Road the nerves vanished. Even in the changing rooms, in the last 20 minutes, I was calm as I could be. My dad said: ‘Take this in, enjoy it. You’ve worked hard to get here.’ I stood there smiling, enjoying it.”

How did he feel an hour later when his name was shouted out as the new world champion? “After being battered for so long, and on a journey for so long, it was amazing. I want to keep that feeling. We’ve made it.”

Warrington has felt pressure since leaving school at 16. “I thought of going into the marines. I then studied sport and psychology but fell out of love with it. I was drifting. My dad knew this guy at the [dental] lab, and he said: ‘Can you give Josh some work?’ I started off as a cleaner. Then I started making models of teeth. A dentist would take an impression of teeth and send it to our lab. I made gumshields and whitening trays. I was enthusiastic and worked my way up to making crowns, and all the realistic fancy false teeth. I really enjoyed the concentration and the detail. It’s quite an art.

Facebook Twitter Pinterest Josh Warrington won the IBF title in a split decision over Lee Selby in May. Photograph: Alex Livesey/Getty Images

“The gaffer said: ‘You’ve got to go to uni.’ So I applied and, having 11 GCSEs, got in. Those were the hardest years. I was working four days a week, studying at uni on my day off, training before and after work. It took four years but I got a diploma in dental technology in 2014.”

Warrington has been a professional for nine years. It has been a long haul but his fanatical following, a flawless 27-0 record and the pay-per-view contest against Frampton on 22 December highlight his belated success. Next month’s bout could be the British fight of the year as the Leeds faithful and Frampton’s army of fans from Belfast descend on Manchester.

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“Beating Carl, who is a genuine world-class boxer, will put me on the world stage. It’s going to be very hard, as he’s a great fighter, but I’m very confident. There is no way I’m going to slag Carl to build a fight. I respect him and we’re both in our prime. We’re going to go at it, hammer and tongs, for my world title. That should be enough, shouldn’t it? We’re not swearing and pushing each other in the buildup. But we’ll have a real scrap.”

Warrington can’t resist a little dig. “In my head I try to see him as this monster Carl Frampton. But when I look into Carl’s eyes, I see a bit of concern. I feel he’s uncertain. He’s concerned about where he is mentally and physically. Is he past his best? Every fighter questions if the fire is still there. But I’m preparing for Carl in peak condition.”

I know Frampton doubts Warrington can match his skill and power and so this match-up between two ferocious competitors and understated men, roared on by their vociferous fans, is compelling. Warrington nods. “My attitude has been right since it changed when I was 22. An old school pal said: ‘Are you looking forward to your next fight?’ I said: ‘Yeah, but I wish I could go out with you boys on the weekend.’ He said: ‘Josh, it’s the same old. We’ve been doing it since we were 18.’ I said: ‘But it’s a laugh.’ He said: ‘All of us would give anything to do what you’re doing. We’re proud of you pal.’ I was like: ‘Wow.’ It made me stand tall. I give everything to boxing now.”

Warrington rubs his battered face and smiles. “Boxing,” he says simply, “is really like nothing else.”

Josh Warrington: Fighting for a City is on DVD and digital download from 26 November