On my way to meet Richard Osman, my eye is caught by the window display in Waterstones on Chiswick High Road. It has the latest from Sally Rooney of course, undoubtedly the dominant millennial author. Next to Rooney is a posthumous novel from John le Carré, arguably the greatest British novelist of his generation. And above them both — in absolute pride of place — is The Man Who Died Twice, the latest cosy crime novel by Osman, that gawky quiz-show bloke off the telly.

How did this happen? Fifteen months ago Osman was a TV producer who hosted shows like Pointless and House of Games.

I've always been aware of him as a jolly sort, droll in a PG sort of way, good at giving Middle Britain a tickle but hardly a literary colossus. Now, though, Osman is the biggest thing to hit publishing since JK Rowling. His publicists like sharing his "major" stats with all and sundry, and who can blame them? The Thursday Murder Club, Osman's 2020 debut novel, was the fastest-selling crime novel of all time, and the second-fastest-selling adult debut novel in history, behind Rowling. He pipped Barack Obama to Christmas No 1 last year and has the third-bestselling fiction hardback of all time, trailing Dan Brown and, well, Rowling. That's major.

The Thursday Murder Club tells the story of Joyce, Ibrahim, Elizabeth and Ron, four residents of Coopers Chase retirement home in Kent, who band together to become a team of amateur murder detectives. Think Cold Case meets One Foot in the Grave. There's something undeniably charming about this motley crew of retirees, a demographic who rarely appear in prime time, taking on cold-blooded killers in the name of justice. It's nicely done, pacey and sharp. But I must admit I didn't quite understand its phenom status.

What is all this extraordinary fuss about? I realise I'd better ask the man himself. I find him wandering the basement of High Road House in Chiswick, a minor Soho House branch where Osman, 51, likes to hang out, because his new house nearby is populated by a working-from-home daughter and "various cats".

We sit down with a cup of earl grey and a biccy, which feels appropriate. Osman is dressed Soho House casual — a grey blazer, blue dad jeans and white Reeboks. He's easy company, so I get straight into it. What does he think is behind this galactic success? "Humans always look for warmth," he says. "There's a reason why Strictly and Bake Off are the two biggest shows on British telly — because they're just lovely. If you can write something that's kind and warm but does have a bit of bite and wit, that's the magic formula."

It sounds a bit trite to me, but I'm not in a position to argue with the guy who's going blow for blow with Harry Potter. Osman is as British as Bird's custard, his books are crammed with references to Robert Dyas and Oliver Bonas, but they're now selling all over the world. The Germans are lapping them up. He's big in Japan. I can hardly compute how many Christmas presents this year will feature Joyce and the gang. Is the pandemic a factor perhaps, people searching for something cuddly and unthreatening in the midst of societal collapse? Osman doesn't love this suggestion. "I think the pandemic thing is a bit of red herring," he says. "I've seen this my whole career. If you make a warm show, people want to watch it. We gravitate towards warmth — not so much in our political narrative, but in our cultural narrative."

The Man Who Died Twice by Richard Osman.

Selling more than two million copies, his first novel was so successful that Osman rapidly cranked out a sequel, which brought the club back together again. The Man Who Died Twice came out this September and sold half a million copies in eight weeks. He has already started writing book three and has a fourth commissioned, so it seems the murder club series will be squatting atop the bestseller lists for years to come. And it will appear on the big screen too: no less than Steven Spielberg is making a movie adaptation of the book, which is due to start filming in the spring and will be directed by oldies whisperer Ol Parker, who did The Best Exotic Marigold Hotel and Mamma Mia! Here We Go Again.

It helps, I think, that Osman has spent his life mastering how to entertain a large audience of bored daytime-TV addicts. This, after all, is the man who produced Deal or No Deal, the show that ravaged an entire generation of hungover undergraduates. This master of middlebrow grew up in Haywards Heath, West Sussex, and has described himself as "southern" but "not posh". He spent much of his career behind the camera, as a producer, and then as creative director for Endemol, producing shows such as Whose Line Is It Anyway? and 8 out of 10 Cats.

He became a TV star in his forties, ending up on camera after impressing BBC executives by playing the role of assistant in the demonstration of the teatime quiz show Pointless. He has co-presented it ever since, along with his old Cambridge University friend Alexander Armstrong. So Osman's carefully curated magic formula — good vibes with just a bit of bite — has been titillating the mass market for 20 years. Now that formula has translated terrifyingly well into fiction that reaches well beyond the typical bookworm and into the great British beyond. "I feel very present in British culture," he says. "I feel very immersed in it. So that's what I wanted to write about."

Osman attends the UK Premiere of Kill Your Friends in 2015. Photo / Getty Images

Not everyone adores Osman's books, though. A reviewer in this newspaper called The Man Who Died Twice's plot "so hackneyed that it is hard to read without yawning", and suggested that The Thursday Murder Club was "so flawed that it is hard to believe it would ever have been published without a celebrity's name on the cover". Ouch. What does he make of the hatchet jobs? "The only thing that upsets you is true criticism," he retorts. "I'm never going to get all the high-brow critics. I'd rather listen to what people in the street are telling me." Osman says even his two twentysomething kids, Ruby and Sonny, are fans. In fact the only criticism that got under his skin was from his mum, who recently told a reporter she finds his writing "quite staccato". "I mean, Mum — come on, Brenda," he chuckles. "She loves Hilary Mantel. I think she'd rather I'd written a sprawling 800-page Tudor epic."

Osman is proud of his middlebrow credentials, though, viewing the word as a compliment and something to be embraced. His Twitter feed is full of musings about Quality Street chocolates, finding fivers in your pocket and his cat, Liesl, while his "perfect Sunday" is a roast dinner, watching the new Bond movie and then curling up with Liesl in front of Strictly Come Dancing. "Middlebrow as an insult I find extraordinary," Osman says. "I'm genuinely, determinedly and proudly middlebrow. I don't have any other options, that's who I am and how I was brought up." His older brother, Mat, is the bassist in the Britpop band Suede and also dabbles in writing fiction novels when he isn't selling out Ally Pally. Mat got all the trendy genes. "My brother is the coolest guy in the world," Osman says. "It's really weird, because he was so cool … but it didn't rub off on me."

Osman dedicated his first book to his mum, as well he might. She raised her two boys as a single parent after their dad walked out when Osman was nine, which he has described as the "worst thing that ever happened" to him. "It adversely affected me for a number of years," he says. "I wasn't real in the world, you manufacture yourself a bit." Osman didn't see his father for 20 years or receive any contact from his father's family — although his aunt has recently claimed they tried. He met his father again before he died, but Osman has described it as a disappointing reunion and not enough to rekindle their relationship. Ultimately Osman realised for his own sake that he had to move beyond anger or resentment. "Is the way you're feeling about it helping you live a happy life? If not, you have to find a way past it. You have to let the toxicity go," he says. "That means forgiving, however infuriating it can feel. I'm utterly at peace with it now."

He characterises his upbringing as "working class" and they managed without a car, getting by on Brenda's teaching salary. It was also his mum's retirement home in Sussex that provided the basis for The Thursday Murder Club. Osman had made a few abortive attempts at a first novel over the years, but it was only when he alighted upon the idea of a murder mystery set in his mum's retirement village that "the radar" in his head went off. Initially his mum was terrified she would get sued when he told her about the idea. Now she's "delighted" with her celebrity status.

So how do the denizens of the real Coopers Chase feel about their new-found fame? "People say the younger generation are obsessed with fame, but that generation absolutely loves it," Osman says. "They love being in the book, which is great. They love it because it's not patronising or mean to them. They recognise that they're the heroes of the story."

Osman grew up devouring Enid Blyton's Famous Five stories, so it is perhaps no surprise that he has found literary fame with a group of inappropriately aged amateur detectives. Part of the books' charm is subverting expectations about the elderly, showing the rest of us that they aren't all just playing bowls and slowly expiring. "They're overlooked, they're underestimated, they're invisible," he says. "And yet they have this extraordinary skill set. So you think, who better to solve a crime?"

Crime stories have always attracted Osman. Post Blyton he didn't read much as a teenager, but picked it up again in his twenties and became a huge fan of Dorothy L Sayers and Agatha Christie, whose Miss Marple he owes an obvious debt to. He thinks Christie's global fame has helped fuel his success beyond Britain. "I'd like to thank her if she was still here."

Crime stories are what he always turns to in the newspaper or when flicking through late-night television, and he already has another radar-tripping idea for a solo detective, which he plans to write about after book four of the murder club series. "You know there are people breaking the law around us as we're sitting here in the leafy streets of Chiswick," he says.

"You know there are people living in £10 million houses because they've got it all in an import-export scam. I find the whole sub-economy fascinating. McMafia. Gangland Britain. I'm endlessly fascinated."

Being a TV celebrity obviously helped Osman get his first novel off the ground, but he says it has also fed his impostor syndrome. When he first approached his agent, Juliet Mushens, who at one point this year had the top three bestsellers in the paperback charts (the other two being Abigail Dean and Claire Douglas), he begged her to tell him if she was only interested because of his fame. "Anyone who has written a first book knows most of your body is screaming out, 'This is terrible and fraudulent,' " he says. "But from the moment someone read it, the whole thing went insane. I'd have been happy just to finish it, but it's been more lovely to sell millions of books than not."

I bet it has. In fact Osman has had a pretty stellar pandemic all round. On top of the books, he has also made countless episodes of House of Games and Pointless, which has kept him occupied. His only professional issue at this point is fitting it all in. "I can't come home after a day of filming and write in the evening," he says. "At the moment it's fine, but it won't be fine for ever. I could imagine rationing myself [on television] a bit more. I've got two things speaking to my soul now and it's not big enough."

Despite his ever-expanding public profile, Osman describes himself as shy and an "alpha introvert", someone who can command a room when he needs to but also often prefers to watch from the corner. "Maybe because my eyesight is terrible, I couldn't fully engage," he says. "I've always had to be more of a spectator, because I'm a bit frightened of the world. I have a tank, which drains. Sometimes I just want to go home and watch the snooker, just be me, sit with my partner and the cat. I'm like a Tesla and there aren't that many charging points around."

The partner is a new development. Osman fell in love last year, and is now living with the Doctor Who actress Ingrid Oliver. There have been other big relationships in Osman's life: with his ex-wife — the mother of his children — and more recently with the jazz singer Sumudu Jayatilaka. But this is "the one", he's reportedly telling friends. "I managed to find love in the pandemic. Sickening, isn't it?" he says with a grin. "I met someone, we love each other and isn't that a wonderful thing? I'm annoyingly, blissfully happy." The pair were introduced by mutual friends, which he says is "the best way" to meet people. "It's been really lovely."

I think "lovely" is Osman's favourite word. I try counting how many times he says it during the interview but lose track at about 15. It's "lovely" to find mega-success in his fifties now that he's mature enough to put the whole thing in context and not get carried away by the influx of cash and attention. "I'm 51, so it's good, I can handle it," he says. "I'm in a position where I say, 'Oh, this is fun.'" It's also "lovely" being a part of the publishing industry's revival, and particularly "lovely" being a recognisable author, so that people can tell him how much they enjoy his books when he's out and about.

In fact he's so relentlessly upbeat that my desiccated inner cynic starts to smell a rat. What's the catch? We all have some inner darkness — what's his? "I don't think I particularly have one," he says. "I don't like queueing. Mild impatience — if that's one of the seven deadly sins, then by God I've got it. I wish I wasn't 6ft 7in with terrible eyesight. That's a cross to bear, but not a particularly big cross."

I'm not sure this is the full story, but Osman admits he often keeps his true self concealed. When dealing with thorny subjects he seems to reach for cookie-cutter aphorisms, telling me "to watch the tides, not the waves" and "you cannot be what you cannot see", which sounds like something one might read on a fridge magnet. "I hide what I really think about the world a lot," he says. "I sit in the centre, but that's not where my heart is." His politics are progressive but he studiously avoids conflict. "I don't think me being a celebrity with an opinion is of interest to anyone," he says. "I don't think responding to every story on Twitter is going to change the world."

It helps no doubt that his anti-culture warrior shtick has been good for business — unlike Rowling he'll never lose fans by taking a sharp political stance. His brand is big friendly giant (or "reluctant lighthouse" as he puts it) and he's unlikely to change course now. "I like to be liked," he says. "That's the part of my personality I try to weaponise. I have zero complacency about the world, but sometimes I like to project that I have complacency. Because people like optimism."

- The Man Who Died Twice by Richard Osman is published by Viking

Written by: Josh Glancy
© The Times of London