London: Even at 51, enveloped by his taint as the most notorious drugs cheat in the history of sport, Ben Johnson has lost none of the old braggadocio.

That searing image of the cheater in the red Canada strip, right arm aloft before he even crossed the finishing line, is at odds with the intense, thickset figure who sits here in the basement of his London hotel and declares his ability to run jaw-dropping times when clean.

“Sprinters were born, not made,” he says, in a West Indian accent richer than Michael Holding voicing a Malibu advert. “The other week I was running a relay in Toronto, and people couldn’t believe how fast I was. I had to tell them, ‘I haven’t trained’. So that’s the talent I have. It’s not about doing drugs.”

But in Johnson’s case it is everything about doing drugs. In September 1988 he was recast in 48 hours from an Olympic 100 metres champion, signing autographs in his white suit at the Seoul Hilton ‘Ben Johnson, fastest man in the world’, to a wretched pariah who had tested positive for stanozolol and awoke to Canadian headlines ranging from ‘Disgrace’ to ‘You B---d’.

As of Friday, he underwent another drastic reinvention, fronting an anti-doping campaign that exhorts the next generation of athletes to “choose the right track”. Either it is an act of bravery or one of supreme brass neck. For while Johnson goes heavy on the contrition, describing his own performance-enhancing path as the “destiny I chose, and that cost me”, he is still excoriating about his enemies.

Of Carl Lewis, who gave the famously dumbstruck stare as he burned down lane six in a steroid-fuelled time of 9.79 seconds, he says: “We don’t like each other, plain and simple. If I say the things that are really on my mind, you won’t like it.” Try me, I say. “He is just there for himself. He might have been the best once, winning gold medals and a lot of money, but he had to move on for somebody else. It was my turn.”

Johnson’s central argument for taking the chemical route is that doping was so rampant in his heyday, competition essentially became a level if perversely distorted playing field. Of the eight men who started that Seoul final, widely dubbed the dirtiest race ever, only two — Calvin Smith, of the United States, and Brazil’s Robson da Silva — were never linked to drugs. Lewis, elevated to the gold medal after Johnson’s disqualification, failed no fewer than three tests at national trials in 1988 but was cleared by the US Olympic Committee. Or, as Johnson puts it: “He tests positive and he gets clearance. I test positive and he gets the gold. There is an unfairness.”

Almost 25 years after his defining disgrace, Johnson remains a darkly compelling figure. He will mark the anniversary on September 24 not by withdrawing into hiding but with a visit to Seoul’s Jamsil Stadium, unfurling a giant anti-doping petition along the lane where he made his burst into infamy.

“It might feel as if, ‘this is where everything happened’,” he says of his return to the scene of the crime. “But that was the first life of Ben Johnson, this is the second. Now I am older, wiser, smarter, stronger.”

The great contradiction about Johnson surrounds the question of just how sorry he is.

On the one hand he invokes the homespun philosophy of his mother Gloria, saying: “She always claimed that the only person I hurt in this world was myself. I didn’t hurt anybody else, didn’t endanger anybody. I never did, never would. I take full responsibility and try to move forward in a positive way.”

But on the other, he purports to be the victim of a vast conspiracy, claiming that his drink was spiked by a “mystery man” in Seoul’s anti-doping room — alleged in his autobiography to be Andre Jackson, a US diamond executive last found working at a mine in Angola. Jackson, invited recently to elaborate on the intrigue, said only: “Of course I can say that I did not. I can also say that I did, too. What would be the benefit?”

When he called his father, Ben Snr, to tell him about the positive test result, the one-word response was: “Americans!” Now, Johnson insists, “I’m someone who wants to fit in with society.” This was an impulse he seldom displayed, though, in the grisly aftermath of Seoul, living remote from the outside world in the Toronto suburb of Newmarket, Ontario, and spending most of his days watching Road Runner cartoons.

His only companion was his mother, who passed away in 2004 and to whom he was utterly devoted.

“The hardest thing I ever faced was to confront my mum,” he remembers. “When I did, she just embraced me and said, ‘At least you have a clear conscience. It’s going to be tough in the years to come but you will get over it. By the time you have dealt with your problems, other people will still have theirs’. I came to understand that, growing up into a man, and I think that what she said 25 years ago is coming to pass.”

Gloria’s words served as Johnson’s solace at a time when all around were disowning him. Pierre Cadieux, a Canadian sports minister, even suggested that he should move back to Jamaica, a comment that he branded “by far the most disgusting I have ever heard”.

But then Johnson did not exactly help himself. In 1991 he attempted a comeback, only to be found guilty two years later of taking excess testosterone and banned for life from athletics. Still he vigorously disputes the finding. “The government didn’t like me, so they tried to tarnish my reputation,” he says. “Looking back, I shouldn’t have come back. I should just have restored my name. But I love to run. It is my passion, my gift.”

It was a gift he assiduously developed from his earliest years in Falmouth, Jamaica, in the Trelawny parish that has since produced Usain Bolt. One of Johnson’s nephews even went to the same school, William Knibb Memorial High, as the greatest sprinter of all.

“I heard of Usain when he was coming through in the juniors,” he recalls. “The drills that I showed to my nephew, he showed to Bolt. But I don’t want to take anything away from him. He has got the talent, and Jamaicans have learnt over the years about the art of peak performance.”

There continue to be doubts about why Jamaica still spends only £400,000 (Dh2.2 million) a year on anti-doping controls — a tiny fraction of a nation such as Norway — not least in light of Asafa Powell’s positive test for a banned stimulant.

A legacy of suspicion has eroded the credibility of the 100m ever since Johnson’s actions, to the point where the eight athletes who lined up in Moscow this month were bracketed, unjustly, as little better than the class of 1988.

Johnson cannot state with certainty how much cleaner his sport has become, but he makes extraordinary assertions about how he could have held his own with Bolt.

In Australia last year he was adamant he was the “greatest sprinter who ever lived”, while announcing that he would have lowered Bolt’s 100m world record of 9.58 seconds to 9.30. Does he stand by this? “Knowing what I do about what is going on out there, that is my answer,” he replies. “Technology has changed over the past 25 years.”

At this point Jaimie Fuller, chairman of Skins, the Swiss-based compression clothing company supporting Johnson’s anti-drugs crusade, interjects, aware that such remarks could be construed as obscene egotism. “The question is Ben’s belief in himself. Nobody achieves at this one-in-six-billion level without being full of confidence. It is incredible.”

Confidence, however, has to be matched with some impression of regret if Johnson is to be taken seriously in his latest guise. He does seem, at least, to regard his past through sorrowful eyes.

“I don’t think it was the right thing to do, but it was brought to my attention that it was what you had to do,” he explains. “I didn’t want to do it, I knew it was wrong. I’m trying to change that way of thinking. I want this generation to go down the decent route.”

Johnson talks of a quieter future, of leaving Toronto to set up a rural home in his native Jamaica. He exhibits, as befits a man raised as a devout Christian who once employed a ‘spiritual adviser’, a greater inner peace. How, then, would he crystallise his Seoul lessons? “Take the right path,” he says, after a pause. “Then everything will take care of itself.”