“This is the most dangerous young man on the planet,” Chris Eubank says in a typically grand way as he gestures towards his son, Chris Jr, who is about to face his first real test in the ring against the unbeaten Billy Joe Saunders at London’s ExCeL Arena on Saturday night. It is a fight between the regal Eubank Jr, who has won all his 18 bouts, and a former Olympian and self-proclaimed hard man of the travelling community who holds the Commonwealth, European and British middleweight titles. They are both 25 and the animosity between them dredges up memories of Eubank Sr’s most bitter and tragic nights against Nigel Benn and Michael Watson in the early 1990s.

Eubank Sr and I go back a long way, for I interviewed him and Watson before their two fights in 1991. Watson had outboxed Eubank in their rematch at White Hart Lane when catastrophe struck. Eubank was knocked down in the 11th round but he hauled himself off the canvas and, somehow, landed a punch of such devastation it resulted in Watson slipping away into a coma that lasted for months. Even today the admirable Watson remains disabled by the consequences.

“That’s why I am telling the referee this week to be vigilant,” Eubank says. “Christopher won’t hesitate and he is the most dangerous man in boxing today. I’ve met all the most dangerous fighters. I fought some of them. As a fighter you can sense and smell it when a person is a certain way. For Saunders and all Christopher’s future opponents the truth is ominous. They are in danger and referees have to be mindful. Christopher has been brought up in the purest form as a fighter. Eccentric, you may call it. Odd, unique, peculiar you may deem it to be. But you have seen nothing like it before.”

Eubank Sr is in rollicking form and it feels like the old days as he regales me with tales of darkness and destruction – in the tortuously modulated manner of a fighter once famous for wearing jodhpurs and a monocle. As always with Eubank it feels best to regard his pronouncements with amused affection, even as he strives to make a serious point. “I’ve looked at Mike Tyson, Nigel Benn, Gerald McClellan and James Toney. They were all dark and they were all great fighters. But they were all were unhinged. You know this. You wrote about me and all of them in Dark Trade. Christopher’s darkness is different. He’s stoic. He’s still. There is a darkness in him I cannot measure.”

Chris Eubank Jr works on the bag. Photograph: Graeme Robertson/Guardian

I look doubtfully at father and son in the crumbling Hove Boxing Club on the seafront. Eubank Jr and I have just completed an intriguing 45-minute interview in which he has been friendly and engaging.

“You’re not wearing boxing gloves,” Eubank Jr says wryly. “In the ring I’m a different animal. You only come out of the dark zone once your hand is raised. I don’t think about the consequences for me or my opponent. It’s one of the reasons I don’t let my mother [Eubank Sr’s ex-wife Karron] come to my fights. I don’t want her in that environment. It’s tunnel vision. If you saw your mum’s face in the crowd, you start thinking: ‘Is she OK?’ I don’t want that. When I’m fighting it’s just search and destroy.”

His father nods sagely. “I am benevolent. I don’t see that in Junior.”

Is he really saying his son is cold and forbidding? “Absolutely. He is charming to interview but they call him arrogant because he fights with an air of majesty, stealth, pizzazz and substance. That’s how I was and people didn’t like it. But I was behaving as a fighter should. I’m supposed to act like a warrior – and that’s what Junior does. But, still, I want to apologise for Christopher’s demeanour in the ring because he cannot be the smiling celebrity type. He is a pure warrior.”

Eubank Jr, like every fighter courageous enough to step inside a ring, is also human and vulnerable. A night will come, possibly even against Saunders, when he is badly hurt. Surely his father will find that hard to bear? “That ought to be the case,” Eubank Sr says, “but I have not seen anyone who has his irrepressibility, relentlessness, speed, power, spite and control. In sparring the other day he hit the guy with 10 uppercuts. And then he changes the angle and lands another six. Then there was a third volley of eight rolling uppercuts. Who does this? I went in the ring with a body protector. He had finished sparring so, effectively, he was spent. But after the first 10 shots he hit me to the body, covered in this bullet‑proof contraption, I walked away and laughed from deep within my stomach – without noise. That’s how hurtful the punches were.

“I don’t know what to make of it. All I can say is that he has been parented in a very peculiar way. I am not a conventional man. I have made citizen arrests in front of him. I have commandeered heavy goods vehicles which were illegally parked in front of him.”

‘Chris is different. He’s stoic. He’s still. There is a darkness in him I cannot measure.’ Photograph: Graeme Robertson/Guardian

Junior must have often sighed, despairingly: “Oh Dad …” Eubank Sr shakes his head. “No. He regarded that as normal behaviour. I am a strong father. The punishments I gave him over the years formed him. Who has inspired that incandescent rage that lives within him? He is shaped by his upbringing and my parenting. It has turned him into a predator.”

I’m more interested in the way in which father and son were cleaved apart when Chris Jr was sent to live in Las Vegas at the age of 16. He did not see his dad much for the next two years. I ask Eubank Jr about those difficult years. “I’ve had the hardest upbringing of any fighter in England,” he says. “I don’t know any other fighter who has gone to a different country on their own and been thrown into the lions’ den. It was do or die. Either go there and flourish or get chewed up and spat back out. I went over there and started to become the fighter I am today in very tough gyms.

“I was being distracted here by silly things – hanging around with the wrong crowd – so I had to get away. Having the Eubank name in England brings lots of pressure. I went to America and flew under the radar. I went to school over there and graduated, but I was the outsider. They hear this accent and they think: ‘What the hell is this guy about?’”

The girls in Vegas probably liked his accent. “Oh, the girls loved it,” Junior says with a grin. “But, at first, people looked at me like I was an alien when I asked: ‘Where’s the bin?’ They’d say: ‘What’s a bin? Oh, a trash can.’ I had to adjust and prove myself.”

Was he lonely? “I’m not that sort of guy,” Eubank Jr says. “I don’t get lonely. Boxing taught me to be on my own. I was only lonely when I lost my first amateur fight at the National Golden Gloves in Detroit. It was my 10th fight and I was beaten by a guy who’d had 100 fights. I was hurt because I’m not a loser. An official had told me the judges were looking for come-forward fighters. So I listened to him and forgot about boxing. I just steamed in, but he was too experienced. I learnt not to listen to anyone after that.”

If the Eubank Sr stamp is all over his son’s career it’s also obvious that Junior has his own mind. During our interview he only looks distant when his dad interrupts to deliver a monologue. Eubank Jr has heard it all before, which is why I’m surprised he allowed his dad to dictate his nonappearance at various press conferences with Saunders. Eubank Sr tells me that, wary of Saunders’ threat to slap Junior, he kept his son away because “he would not be safe from reputational jeopardy …”

‘I am a strong father. The punishments I gave him over the years formed him. Who has inspired that incandescent rage that lives within him? He is shaped by his upbringing and my parenting. It has turned him into a predator’ Photograph: Graeme Robertson/Guardian

Eubank Jr speaks more plainly. “We haven’t done any press conferences because this guy disgraces boxing. We don’t want to be associated with him. He doesn’t act like a champion so we’re not treating him like one.”

“Exactly!” his father says. “He may have the belts but he swears in front of his six‑year‑old son.”

Does Eubank Jr respect Saunders as a fighter? “I respect every man who climbs through those ropes. But as a person he’s a disgrace. He has a genuine dislike for me – whether it’s because of the kind of fighter I am, who puts on a show, or because I’m one of the most recognised names in British boxing. Maybe he feels he should be in my position. But he’s a basic fighter, which is why I call him Average Joe.”

Saunders, however, is much skilful than any of the journeymen and no-hopers who feature on Eubank’s record. “He’s definitely at a higher level than anyone else I’ve faced as a professional,” Eubank Jr agrees. “But in terms of those I’ve sparred with he doesn’t come close. I’ve shared the ring with world champions and held my own. Carl Froch, Nathan Cleverly, George Groves, David Haye, [James] DeGale and, in the States, Chad Dawson, Montell Griffin and Zab Judah. These are serious fighters and countless levels above Average Joe. He says he wants to kill me. But he knows he can’t beat me.”

Eubank Jr has watched many of his father’s fights over and over again – “to see what you need to become a world champion”. He admires his dad most in his ferocious first battle against Nigel Benn – which happened 24 years ago this month. “Everyone doubted him. But he knew he would beat Benn. It’s similar to now. Saunders is the undefeated champion and I’ve not fought at his level. I’ve not gone 12 rounds. I’ve only ever gone eight rounds. So people don’t know what to expect – which is why it will be even more special when I take him out.”

It’s unlikely to be as brutal as his father’s encounter with Benn. “No. I don’t think he has the heart or resolve to trade with me. If I’m wrong it could be a Fight of the Year – if he’s willing to take his punishment and try to give some back. But he’s got amateur pedigree and he punches to score points. I punch to break my opponent’s will and take him out.”

Eubank Sr exclaims his approval with a wordless roar. “You see?” he says. “I told you. He is a pure warrior. If he was not a boxer I could have given him fatherly love.” The 48-year-old smiles enigmatically. “Perhaps I can’t really offer that love because I am a warrior. I am tough. I am relentless. It suits me that he is a fighter – because I can teach him to stand alone.”

I ask Eubank Jr if he wishes his father could just be his dad – instead of a “pure warrior” and pontificating philosopher? “He’s always my dad,” Junior says simply; Eubank Sr positively beams. “Once you become a fighter, if you are pure, you don’t change. Outside the ring [in retirement] you use your force only by intellect – never physicality. No matter how intelligent you may be you are subtle and transparent. You do not use machiavellian skills. You remain noble. People today may have an obscure view of boxing but it taught me to be calm, gentle and true.”

An afternoon with Eubank Sr is still like nothing else in boxing – and a strange silence settles over the gym when he finally departs. Four of us are left to soak up the quiet. Eubank Jr pummels a heavy bag while his sister, Emily, crouches down and photographs him at work. At the opposite end of the gym I sit with Ronnie Davies, the craggy-faced 68-year-old who trained Eubank Sr and now Eubank Jr. Davies and I are back where we were before those fights against Benn and Watson.

‘An afternoon with Eubank Sr is still like nothing else in boxing – and a strange silence settles over the gym when he finally departs.’ Photograph: Graeme Robertson/Guardian

I still don’t know how good Eubank Jr may be amid his father’s rhetoric. The most dangerous man in the middleweight division, and all of boxing, is Gennady Golovkin . But I listen closely while Davies describes, in stark language, how Eubank Jr thrived in gym wars against Froch, Groves and DeGale. “He’s seriously good,” Davies says. “But just a little hard to reach. He’s got something different.”

It is the closest Davies comes to echoing the “spiteful darkness” that Eubank Sr hails in his son – but as we watch the sweat fly from him it’s possible to imagine a new champion might emerge on Saturday night. Saunders has much more experience but, as Davies says quietly: “He’s fighting a Eubank. He’ll discover something I’ve known for over 25 years. There ain’t nothing like a Eubank in the ring. Billy Joe could be in for one hell of a shock.”

Eubank Jr v Saunders is live on BoxNation this Saturday (Sky 437/490HD, Virgin 546, TalkTalk 525). Subscribe at boxnation.com