Despite huge success as a crime novelist, Richard Osman admits it’s “absolutely terrifying” when other people read his books for the first time.

In fact, Osman – whose new title, The Last Devil to Die, has just become the fastest-selling hardback novel by a British author in history – won’t even let his new wife read them until they’ve been officially proof read.

“When someone else reads my books for the first time, it’s absolutely terrifying, every single time. Every time, you think: I’ve done something horribly wrong, or they’re going to see through me this time.

“Every response you get, you’re trying to read between the lines – do they hate it? That bit when you first send it off, it’s mortifying.”

He’s aghast at the thought of reading any reviews. “Of course I don’t read them – I’ve not read a single review, nor will I. You have to trust yourself and trust your readers, I think. I’ve had enough reviews over my TV career to know to ignore them.”

As for his wife, actress Ingrid Oliver (they got married in December last year), he says: “My wife won’t read it until it’s been properly proof read, because otherwise she’ll just be looking for spelling mistakes and commas and can’t enjoy the book.”

He’s quick to add, however: “We’re very big supporters of each other’s careers, which is lovely. I’m a huge fan of hers, and she appears to be a huge fan of mine up to now.

“But she’s incredibly supportive, and also just incredibly useful in the creative process as well – she understands.”

Osman, 52, who first became a household name as the presenter of hit TV shows like Pointless and House Of Games, clearly has no solid reason to be so doubtful of his writing. The first of his four-novel Thursday Murder Club series became a platinum bestseller with over a million copies sold in the UK, and Steven Spielberg’s production company has even snapped up the film rights.

The Last Devil to Die – the fourth book in the series – sold a record-breaking 146,919 hardback copies in its first week of sales this month.

The book is the latest crime-fighting adventure for a group of intrepid pensioners who live in a Kent retirement village. The new tale features drug dealing (which Osman is at pains to point out he did not try to research), art forgery, a mounting body count and even, as this is about a group of elderly people and Osman is determined to tackle real issues, dementia.

Although he loves the fun and mischief his golden oldies enjoy in his books, “these accounts have to be true, and if you’re older then it does bring infirmity, it brings grief, there’s death around, and dementia,” he adds. “So I have to write about those things if I’m writing older characters, because I have to write the truth of how they live.”

He says both his grandparents had dementia. “So many families across Britain have gone through or are going through it – it touches everybody. I just wanted to write about it with some dignity and humanity, and thus far, people are responding to it really well.”

It’s not often that the heroes and heroines in a murder mystery tale are pensioners. Osman explains that the inspiration was his mum and her friends. “When I saw them, I thought this is an invisible generation, and firstly, I’d like to put that right. But secondly, if you’re invisible, you make a great detective. So I took advantage of the fact they’re an invisible generation.

“The second I started writing them, I just fell in love with them,” he continues. “When you’re writing, you have to start with the characters – you can make it as exciting as possible and have a great plot, but if you don’t have characters who people care about, then no one’s interested. You have to want to follow these people.”

Sadly for fans of the Thursday Murder Club, The Last Devil To Die will be the last book in the series for a year or so, as Osman is writing a new, different series. But don’t despair – he promises the gang will return eventually.

“By the time you get to the end of this book, I think you’d say they deserve a year off, so I’m putting them on sabbatical for a year, giving them a bit of rest and recuperation,” Osman says with a chuckle. “I’m writing a new series next, but the Thursday Murder Club will be back, stronger than ever.”

He’s already started writing the new novels, and admits: “I’m in the very early stages of the writing process, which is always a terrifying place to be.”

This terror isn’t so much about thinking up new ideas, rather how readers will receive the new characters.

“My whole career has been about ideas, so I never worry about them. What I spend all my time thinking about is who are these characters? Do we like them? If I put them through something awful will people care?

“If I have an idea, I immediately shape it and form it and polish it, until it’s something people will love. That’s the general test – think of something, and then think how do I present this in a way the public will love and that will entertain people? Entertaining people is essentially the gist of my career thus far.”

He still presents House Of Games – “which I absolutely love and I’m not going to give up” – but “100%” think of himself now as a novelist. It’s challenging, though.

“Creating is the hardest thing I’ve ever done, genuinely – the creative equivalent of running a marathon. It’s very difficult, and at the start of each one, it seems impossible,” he says.

“You know how you never, ever want to go to the gym? So your whole day is, how am I going to put this off? And then at some point, the trainers are on, and that’s it, you’ve got to go to the gym. Writing is like that – I will find any excuse to not go and sit down, anything. But once I do, then I’ll do two, three hours – I try and do 1,500 words or a chapter each time.

“So once I’ve sat down, I’m disciplined, I’m good. No distractions or floating off, no internet. There’s a cat, but that’s my only entertainment. But oh my goodness, I will come up with any excuse not to write – I’m so ill-disciplined.”

He loves “hanging out” with other writers at crime writing festivals, modestly admitting: “I’m so excited to be in their company – but I have to pretend to be cool when I’m with Val McDermid or Mick Herron or people like that who are just absolute heroes.

“It’s lovely meeting other writers –  I met Lee Child recently, and Harlan Coben, and it’s great to know that they find it difficult as well. That’s why the achievement feels so good when you finish.

“Some days are great and some days are awful, like any job. But I can’t think of a single writer I know who would say they actually enjoy the process – it’s really hard.

“But there are moments, of course, when you read something back and you find yourself laughing or crying, or just thinking: ‘You know what, I think I’ve nailed it’.”

The Last Devil To Die by Richard Osman is published by Viking, priced £22 in hardback. Available now.