Anthony Joshua, the Hertfordshire bricklayer who has become British boxing’s greatest star, is a busy boy. After months of trying to find a gap in his schedule, we finally isolate a weekend in Watford. Within 24 hours, that’s shifted to a Friday in Sheffield, and a modern, unremarkable cul-de-sac on the edge of town. Here, in what appears to be a block of student accommodation, I almost trip over my 6ft 6in interviewee, who is doing stretches on the floor in the middle of a cluttered sitting room-cum-kitchen. Around the place, his team squat on beanbags, scrolling through their phones and sharing jokes; on a flat-pack table are stacked plastic boxes filled with the day’s meals. This, surely, is not the stuff of boxing legend.

I don’t need to be around all the man dem, all the boys, to have my character or be respected

Don’t be fooled. A month out from his fight with Wladimir Klitschko – or “Doctor Steelhammer”, as he is also known – 27-year-old Joshua is leaving nothing to chance. The relaxed surroundings aren’t a sign of his complacency about taking on a 41-year-old whose last fight, against Tyson Fury in 2015, ended in defeat; they’re about stripping it back to basics. “My new saying at the minute,” he tells me, “is: ‘I’m grinding like it’s 2005’” – the year he was still on civvy street, yet to step into a boxing ring.

It’s 10am, and Joshua has returned from his four-mile canal run (days after we meet he posts a picture of himself shadow-boxing on the towpath on Instagram; the Daily Mail reports it, such is the interest in him). For all the world as if he’s slipping into a pair of comfy old jeans, he puts on an extraordinary contraption – compression trousers that inflate and deflate like a blood pressure cuff, wheezing gently, and settles down to talk.

So, I ask. You’re in digs, you train at a public facility where it can take you a while to get through the crowds to your session. What’s that all about? He laughs. “Yeah, we’re accessible, which is good. I think being a boxer you have to be a man of the people. It’s old-school, isn’t it? When you think of boxing, you think of the Rocky films, you know what I mean?”

Golden gloves: Joshua defeats Italy’s Roberto Cammarelle to win the men’s super heavy final at the London Olympics. Photograph: Scott Heavey/Getty Images

The Rocky reference is interesting. He captioned that Insta picture: “My Rocky IV moment.” Joshua did not grow up obsessed by boxing, watching re-runs of the great bouts. “Never watched it,” he says. “Not into sport.” He clarifies. “I like the entertainment. I would definitely watch football. I would go with my pals to watch a game. I’m not against it. But for some reason I don’t understand how the leagues work and what’s the point in playing friendlies? I’m not going to go and sell out Wembley to have a friendly fight with Klitschko.” He roars with laughter.

I’d rather choose certainty over the love of something. I’m looking for the certain wins

There’s a paradox emerging: Joshua is exceptionally committed. For the foreseeable future his life is “ring, ring, ring”. No time for girlfriends, no parties, no clubs, no celebrity hi-jinks. Indeed, he still lives with his mum, social worker Yeta Odusanya, in Golders Green, north London. He has an infant son, with former partner Nicole Osbourne, but thinks of retirement as the point when he will really be able to spend time with him. The team he’s assembled around him – from Eddie Hearn’s Matchroom Boxing to his coach Rob McCracken, trainers, PR people, and the friends who accompany him – is a slick operation.

He is frequently spoken about as a new breed of professional: organised, forward-thinking, tipped to amass serious amounts of money. Despite a couple of brushes with the law (fighting, which saw him put on remand in Reading prison in 2009, possibly its most famous inmate since Oscar Wilde; possession of cannabis in 2011, made slightly worse by the fact he was wearing his GB Boxing tracksuit when he was busted), he is pretty clean-cut.

Joshua does not throw tables in press conferences, nor indulge in much trash talk at all. A recent social media “furore” which resulted when he posted a picture of himself praying in a mosque in Dubai – he is not a Muslim, but was with a friend who was, and likes the idea of embracing other cultures and religions in a show of unity – saw him gain 16,000 followers in 24 hours, and numerous expressions of support in the face of the anti-Muslim bile that had greeted the original tweet.

Heavy hitters: Anthony Joshua vs Wladimir Klitschko press conference at Wembley Stadium ahead of their fight. Photograph: Andy Rain/EPA

He is, in other words, a marketing man’s dream, which has allowed Hearn to circumvent the disappearance of boxing from terrestrial TV. There are many top-flight boxers who could walk into a pub and go completely unrecognised. Joshua is not one of them.

But here’s the paradox. He was 18 before he even thought about boxing, had his first amateur fight in 2007, and won super-heavyweight gold at the London Olympics in 2012. He turned pro less than four years ago. Not only has he never lost a fight in his professional career, but he has always knocked his opponents out; only two fighters have ever taken him beyond the third round. How has this happened?

One answer is Mike Tyson, Joshua’s great inspiration (he hastens to add that he’s not including his behaviour outside the ring). As a teenager in Watford, Joshua – then known by the name Femi, a shortening of one of his middle names – hung around with a big group that stuck close and moved as one. His parents had both moved from Nigeria to Watford as young adults, and the family – he has two sisters and a brother – lived on the Meriden Estate. In a Sky Sports documentary, he spoke of an exceptionally happy upbringing. He knew everyone, including friend of a friend Geri Halliwell, played football, drank in the local pub. But eventually it led to trouble: fighting, setting fires, becoming known to the police. He even, he tells me, used to smoke. When his parents moved to London, he remained in Watford and its hostels, but finally, he was more or less forced to move away.

He might not have thought it at the time, but it was a form of liberation. “I wanted to show that as an individual thinker I can achieve on my own,” he explains. “I don’t need to be around all the man dem, all the boys, to have my character or be respected.” He started to lift weights, became motivated by “purifying” himself. He was spending a lot of time with his cousin, Ben Ileyemi, now also a professional boxer, and Ben kept asking him to come along to the Finchley & District Amateur Boxing Club with him. Again, Joshua wasn’t particularly tempted, and eventually went along more to fall in with his cousin than anything else.

He began to see how boxing made him better in the gym, and sharpened his fitness. And he started thinking about Tyson and how he “built his own empire”. Joshua, who, when he was working in the building trade, used to plan how he’d move on to driveways, barbecues, outhouses, bungalow conversions and eventually build up his own business, started “strategising how I could take this to the next level”.

On a high: Joshua celebrates after defeating Charles Martin to take the IBF Heavyweight title on 9 April 2016. Photograph: Richard Heathcote/Getty Images

What struck him about Tyson, he says now, was that he was just an ordinary kid: “He wasn’t always a boxer. They took him from troubled circumstances, took him to a boxing gym, the team around him developed this kid, and he became one of the most feared heavyweights that the world’s ever seen. So I just saw that it’s like manufacturing someone. So when I went into boxing, I saw that if I worked hard and surrounded myself with the right people, and dedicated myself, I could manufacture myself to become a good fighter.”

To aid that process, he adheres to the thoroughly modern mantra that every challenge is a learning opportunity. His route into the sport, he explains, has actually worked out well for him because now boxing is “all I know. And as the years have gone on, it’s just who I’ve become, so I have to act as if I belong here, because this is what I’ve chosen to do. So that’s the motivation. I can’t fall back on anything, because I’m starting too late. I have to put my eggs in this basket now and ride out the wave, ride out the storm.”

There are caveats, of course, to the idea of the boxer constructed as if he were a boy band. In a world of heavyweight giants, Joshua combines muscularity, athleticism and speed to outwit his opponents. Unlike the East European boxing scene out of which the Klitschkos came, with its more static, jab-dependent style. Joshua is mobile, fleet. He is not over-muscled (although, frankly, I wouldn’t want to iron the tailor-made shirts he’s fond of). And, to state the obvious, he has a very good punch.

‘I always go for the knockout’: Anthony Joshua shot for OM at The Grove, Hertforshire. Styling Hope Lawrie. Suit jacket £400 and waistcoat £160, both Hugo Boss at mrporter.com . White shirt £189, Canali at harrods.com . Tie £125 drakes.com

As a fledgeling fighter, he used to get up at 3am to jog, thinking that every bit extra helped (I’m reminded of Daley Thompson’s insistence on training on Christmas Day on the grounds that you gained two days over your rivals; the work you did and the work they didn’t). Now, Joshua and his team have refined his daily schedule so his various sessions are reduced and he can spend enough time resting and recuperating. He loves a nap and pities those who can’t fall asleep in the day.

The priority is efficiency, return on investment. “It’s all about the hustle,” Joshua tells me. “The hustle is about the long term. It’s not about a quick fix. I’m not after a sugar rush, when you spike up and then you’re back down. I would rather choose certainty over the love of something. I’m looking for the certain wins. I don’t do it because I like it, and when I’m just like, this is fun for now. Scrap that. What’s going to work? I will go through the dirt and grind for the long-term gain.”

Fans want me to get battered for 11 rounds then come back. They want to see how far I’ll dig to get to my goal

You could read this and get a sense of someone cold, driven only by financial success and the pursuit of fame, but that’s not how he comes across; and, of course, that’s also a romanticised and nostalgic stereotype of how sports people work. Sure, when Joshua describes the early days, he says that “I just wanted to make money”; but winning obviously means more to him than that. I ask him about the complex business of title unification across the three boxing organisations and the idea that he could be a supreme champion, and he replies: “Yeah. But funnily enough, it’s more about happiness. The belts never represented me. I was me before the belts. I was this same person, hungry, determined, before the belts. So the unification is part of the process, but the goal is that when I naturally leave this position that I’m in, I will still sit as a happy man.”

I also tell him that the hierarchies and organisations are the thing I find most baffling about boxing. “I don’t even know how to score a fight!” he jokes. “That’s why I go for the knockout. You may write about it, but you don’t have to understand the whole thing. Don’t worry about it.”

So how is he feeling about Wembley on 29 April? Klitschko might be significantly older, but he is also boxing royalty, having held all three world titles and lost only four out of 68 professional fights. Joshua insists he doesn’t underestimate his opponent and, consistent with his own approach of turning negatives into positives, cites Klitschko’s age as one of the reasons. “It’s tough for me now and I’m younger. Imagine: I’m around people of his age, and I think to myself, they couldn’t do it. So I think to myself, I wonder what he’s doing. He must be in a place, mentally, where he wants to do it.”

Given that Joshua is not only unbeaten but also extremely economical in victories, I wonder if he can even conceptualise the idea of defeat. He goes a little bit Hallmark card – all losses are wins really because you learn, etc – but actually what I think he’s saying is that if he did lose, now or in the future, he’d take it on the chin. The urge to fight is, he says, too strong to resist until his body gives out.

Will he still be climbing into the ring when he’s 41? He doesn’t rule it out, although he thinks 37 or 38 is a more natural time to call it a day. And he certainly hasn’t begun to think about what he might do with his life. After all, as he points out, there are only so many beaches you can sit on, only so many public appearances you can make.

But there’s a lot more fighting to do before then. One of the issues for Joshua has been finding serious enough competition. “Yeah, people love it,” he says. “That’s what they want to see. They want to see me get battered for 11 rounds and come back. They want to see how far you will dig to get to your goal.”

To that end, the afternoon we meet he’ll be taking on two ranked pros, both of whom have flown in for the day. The pair fight four rounds each, turn and turn about, so Joshua is always faced with a fresh man; one of them is 6ft 9in.

Will preparation like that be enough come fight day? “The event’s bigger, but the ring remains the same,” says Joshua. “The objective is still to win. My training is due diligence, so I don’t want to go in there and start making it more complicated than it really is. Just got to do the job, and remain as confident as I always am.”

As I gather my stuff to leave, Joshua starts assembling his midday meal – a pile of pasta, something brown and pulse-like, and a couple of hard-boiled eggs. Not raw, like in Rocky? “No,” he replies, peeling them. “I never know why he did that. I tried it, but I just wasn’t feeling it.”

Anthony Joshua faces Wladimir Klitschko at Wembley Stadium on 29 April