Rob Rinder – former barrister, now broadcaster – is contemplating how his friend, actor Benedict Cumberbatch, could be an ideal choice to star in a TV adaptation of his debut courtroom page-turner, The Trial.

The TV legal eagle, who made his name in reality court show Judge Rinder and who is starring in the fifth series of Amazing Hotels: Life Beyond The Lobby with top chef Monica Galetti later this year, recalls how Cumberbatch, whom he met at Manchester University, was the man who deterred him from pursuing a career in acting.

“I’d been to the National Youth Theatre at 14 but when I arrived at university I did one play. I auditioned for it and thought, the person who read after me (Cumberbatch) was so good. It was almost like hearing music in a different way, where I’m an amateur pianist and conduct a bit and then you watch someone really good do it and you think, that’s what it’s supposed to be like.

“Frankly, if I’d have networked really well I might have been able to get the odd bit part, perhaps in Eldorado.”

Now, he has turned his legal experience into his debut novel, a holiday page-turner which begins with celebrity copper, DI Grant Cliveden, dropping dead at the Old Bailey from botulinum toxin, poisoning. The main suspect, a career criminal who served 10 years for armed robbery, swears he didn’t do it.

It is left to trainee barrister Adam Green to defend him and, as he digs deeper, he finds a host of other suspects who had motives to kill the inspector.

The book, which is peppered with humour as the young barrister endures phone calls from his fussy mother who wants to find him a girlfriend, has already been optioned for TV, which has delighted Rinder, who wonders who might play the naïve but persistent rookie.

What about Ben Whishaw? “I mean, I agree, he was so wonderful in This Is Going To Hurt. Adam (Kay) wrote that book from real lived experience as a junior doctor and has all of those genuine and authentic memories.”

His own memories of his time as a barrister are also relived in The Trial. At one point, Green secures a conditional discharge for a shoplifter, only for the grateful criminal to go to the shop next door to steal a box of chocolates for him as a thank you. That actually happened to one of Rinder’s friends, he recalls.

“You very quickly normalise things that are not normal, be they spending a lot of time with violence or dead bodies, at the piercing edge of human behaviour and experience, and you gradually get surgeons’ or gallows humour.”

Rinder, 45, has long been a fan of crime fiction, having read all of John Grisham’s novels and is an Agatha Christie aficionado.

He’s fascinated with poison – and a lethal dose of botulinum toxin, slipped in a drink and ingested, might be difficult to detect, he says, not to be confused with the miniscule quantities injected to stop wrinkles.

“Poison is a woman’s weapon and Agatha Christie is practically an apothecary of knowledge when it came to the sort of things that would kill you.”

He says that all his stories from chambers are as true as he can make them without being sued by anybody, but come from real experience.

He hopes it’s going to be the first of a series and has already started penning his second novel, set in the world of daytime television, in which a well-known female TV presenter is murdered and a chef goes on trial for the crime.

He’s still a member of his chambers. “I can’t do jury trials, but I try to answer questions every week, I still teach a little and I still mentor and try to provide a platform and support for public legal cases, whether that’s being an ambassador for Shelter or taking on private cases in an advisory role. My special interest is international law and the movement of criminal money.”

He doesn’t feel that moving into TV has reduced his gravitas as an expert in the legal profession.

“If you think about Judge Rinder, you could think there are cases on there which are perhaps a bit silly, but at the core of everything we [did] they were real cases, real law, and I cared genuinely deeply and still do about where people would come to court in often toxic conflict and leave having heard one another, perhaps having had an understanding of what their legal rights were, and that ultimately they should settle whatever issue that was in a way which would best deliver long-term happiness.”

He has appeared on a number of TV shows, including Room 101, Celebrity Who Wants To Be A Millionaire, Strictly Come Dancing, Good Morning Britain and Celebrity Gogglebox, and has recently been filming a new series with Rylan Clark, exploring Italy.

“You call it fame, I call it privilege. People are really nice to me. You improve the chemistry of someone’s day just by smiling for a selfie. If you won’t do that, frankly you should get yourself another job.”

The Trial by Rob Rinder is published by Century, priced £20. Available now