One evening in 2008, Stephen Kelman was watching a documentary about India on television in which the actor, writer and broadcaster Paul Merton kicked a man called Bibhuti Bhushan Nayak in the groin.

The Booker Prize shortlisted novelist says, with some emotion, that that eye-watering moment changed his life for ever. Indeed, in his unique second novel, Man On Fire, which he’ll be discussing at the Edinburgh International Book Festival, he acknowledges his debt. He writes: “I’d like to thank Paul for accepting Bibhuti’s invitation to kick him in the groin, an act of grace and bravery from which this book and a life-changing friendship eventually emerged.”

Man On Fire, an enthralling fictionalised part-biography of Bibhuti, is Kelman’s moving tribute to the Times of India journalist, fitness freak, vegetarian, community activist and serial world record breaker, who has pushed himself to the limits of extreme endurance by smashing records for – among many others – the number of kicks to the unprotected groin in one minute-and-a half (43); or doing the most stomach sit-ups in one hour (1,448); or having water melons dropped on his stomach in one minute from a height of 10m (31).

“You can’t call what Bibhuti does sport. He’s 50-years-old now yet only weeks ago he broke another three world records – including for the most alternate squat thrusts in a minute,” says Kelman, whose bestselling debut novel, Pigeon English, was shortlisted for six major literary prizes and is now a set text on the GCSE syllabus. That book was inspired by the story of Damilola Taylor, the young Nigerian boy, new to England, killed by two teenagers in London, in 2000.

Luton-born and raised on the tough Marsh Farm council estate, 39-year-old Kelman – no relation to James, although he shares the great Glaswegian’s ability to write dark, gut-wrenching books full of life and energy, and that are often very funny – was fired up after seeing this larger-than-life personality. “He was so completely at ease and at peace with himself, while inviting someone to kick him in the testicles on television.” Here was a man – some call him “India’s Bruce Lee” – who had apparently discovered how to conquer pain.

Kelman knew immediately he wanted to write about him. “He was such an interesting character. I felt I wanted to take him apart, find out what makes him tick.”

A week after he saw Bibhuti on television, Kelman received his first email from him. “I told him I was an unpublished author, but that I’d love to tell his story. At the time I was only dreaming of becoming a writer while working in local government. I was dabbling in screenplays, because I had this bizarre idea that they were easier and quicker to write than novels. That may be true but they are certainly not easier to sell,” he confesses when we meet in his publisher’s London offices, because he dislikes being interviewed in public. “I prefer being low-key,” he says.

“I asked Bibhuti for permission to tell his story. He’s such a gracious man, he gave his consent right away. He said I’d obviously seen something in him that had spoken to me. He knew I would need to fictionalise and play around with the facts, but he was overwhelmed that I had been moved enough by him to actually think I could tell his story. He took a chance on me. For two years we emailed back and forth.”

The question I have been longing to ask this thoughtful, immensely likeable, modest man is whether he has since kicked his inspirational, profoundly spiritual friend in the groin. “No, I haven’t,” he replies. “Maybe it will become one of the great regrets of my life. Who knows? But we get on well enough without the need for me to kick him in the balls.”

Man On Fire is narrated in the first-person by two voices: Bibhuti and the fictional John Lock, a 60-year-old Englishman, who flees from his quiet, dead-end life, boring job and desperately sad, fractured marriage, to India to help Bibhuti with his latest world record attempt: to have 50 baseball bats smashed over his body. The result is, as Roddy Doyle notes in a dust jacket blurb, “a glorious, warm, unpredictable story, told by two glorious, warm unpredictable narrators. I loved it!”

I tell Kelman that I loved it, too, that I have never read a book quite like it. “That means a lot to me, especially when you say how original you found it. There were a lot of expectations that, with my second book, I would repeat Pigeon English, that I would stay in that world [working-class council estates], which doesn’t get written about in fiction, that I would continue to plough that furrow, although I am still very much of that world myself. Much as I love Pigeon English, to which people responded in a very powerful way, I wanted to write a book that was completely different, so I felt an awful lot of pressure writing Man On Fire. It took about three times longer to write than Pigeon English.

“With the early drafts of Man On Fire, I realised I was trying too hard, that I had to take a step back and that coincided with all the promotional stuff for Pigeon English. So I took a break, deciding what writer I wanted to be. I’ve completed it, I think, with a greater sense of simplicity. My job is to tell the story truthfully, both Bibhuti’s and John Lock’s since he was inspired by my own father. John is suffering from cancer and I have watched my dad, now 75, cope with great dignity and courage after being diagnosed with cancer more than three years ago.”

Before the novel, there was the screenplay. Kelman could not sell it, much to his disappointment, but decided to write a novel, about Bibhuti, that would also be a partial biography. First, though, he wrote Pigeon English, told through the eyes of Harri, an 11-year-old Ghanaian boy, whose voice “just came” to him one day. The book is partly a tribute to Damilola Taylor and all the other children who lost their lives in what seemed to be an epidemic of child-on-child violence in urban Britain. “I just wanted to get Pigeon English out of me, although I had no hope it would ever get published.”

He was wrong. His manuscript was plucked from a slush pile. There was a bidding war between 12 publishers and Bloomsbury won the rights, with their “six-figure” offer. Before he knew it, Kelman was “gatecrashing” the Booker. He had, though, promised Bibhuti that the first thing he would do once he got his advance was travel to his Navi Mumbai home to meet him and finally write about him.

“I kept my promise,” says Kelman, who has dedicated Man On Fire to Bibhuti, his own parents and his wife, Uzma, who he first met at primary school. “We sat next to each other and became friends. I never saw her for 25 years, but then we found each other and married in 2011.”

They had a lot of catching up to do. After graduating from the University of Bedfordshire, Kelman drifted from one boring job to another because he had known he wanted to write since he was six-years-old when he began writing short stories. As a child he was a precocious reader, encouraged by loving parents, grandparents and two exceptional teachers. “Reading for pleasure was not culturally accepted when I was growing up. Nobody went to theatres, art galleries or museums. If you let it slip you enjoyed that cultural life, you were targeted. That went on throughout my childhood. My writing became my guilty secret even from the family. I thought they might think it silly.”

It’s an open secret now, although he still regards his success with a measure of disbelief, and has a drawerful of screenplays and a first novel that will never see the light of day. “It got rejected several times, but I just kept going. I think I was waiting for the right story,” he says, adding that he could never have made up a character such as Bibhuti Bushhan Nayak, his “pathfinder”.

Meanwhile, Bibhuti, who is thrilled with Man On Fire, presented him with a personalised fitness and breathing regime when they last met in India in October. “Follow this two or three times a day and within a few months you will have a six-pack and feel ten years younger,” Bibhuti told him.

How is the six-pack? “I’m taking the fifth amendment. Readers like a sense of mystery – let’s just say it’s a four-pack.”

Man On Fire is published by Bloomsbury Circus, £12.99. Stephen Kelman is at the Edinburgh International Book Festival on August 15.