Martin Clunes interview: The actor stars as the Sherlock Holmes creator in Arthur & George

The new ITV drama focuses on a tale of a miscarriage of justice fuelled by racial prejudice. He tells Gerard Gilbert about a curious case

"When I tell people I'm playing Arthur Conan Doyle on TV, some of them ask, 'Oh, is Benedict Cumberbatch in it?'," says Martin Clunes, illustrating a common blurring of distinction between the creator of Sherlock Holmes and his creation. Sitting in a carriage on a steam train on the Bluebell Railway line in Sussex (the same locomotives used in Downton Abbey, as it happens), with Clunes suited, booted and cloaked in full Victorian-Holmesian outwear, it's easy to understand the confusion. "London taxi drivers tell me that American tourists have sort of heard of Conan Doyle," he says, as we chug through the countryside, "but they think he was a prime minister. Mind you, they also think Sherlock was prime minister."

So to be clear: Clunes is filming a scene in ITV's new three-hour adaptation of Julian Barnes's 2005 novel Arthur & George, in which Barnes fictionalised real events from 1903 when Conan Doyle – rich and famous from the proceeds of his Sherlock Holmes stories, but widowed and bored – took it on himself to investigate what he saw as a miscarriage of justice. Staffordshire solicitor George Edalji, the Anglo-Indian son of a vicar – and the victim apparently of long-standing racial prejudice – had been convicted of mutilating livestock. "There's no way he could have cut those animals," says Clunes. "He was a bookish, disabled, poor-eye-sighted solicitor."

Clunes's wife, and the co-owner of a production company that also makes the actor's enduring ITV hit Doc Martin, Philippa Braithwaite, optioned Barnes's novel – with no real intention, she tells me, of casting her husband as Conan Doyle. "It wasn't written for Martin; it was just because I loved the book," she says. "I didn't know anything about Conan Doyle. I just picked up this book and it was a real case that just seemed so bizarre. And this was before any of the big Sherlock Holmes revivals had started really, so it was a coincidence that Sherlock had become so huge while we were working on this."

"I knew she was beavering away on this and slugging it out with Julian Barnes's agent and trying to satisfy them," says Clunes. "When I read the book I couldn't instantly see what Philippa had seen because it doesn't scream out 'televise me' when you read it, but she's obviously much smarter than I am." Peter Fincham, director of television at ITV, had, in his previous job as controller of BBC1, tried to persuade the channel to film Barnes's novel, but had been told it was "BBC2". "In the way that people say those things," says Clunes.

TV thriller veteran Ed Whitmore, who has written for the likes of Silent Witness and Waking the Dead, was hired to give Barnes's novel more of a contemporary-thriller edge and has pared it down by about two thirds, omitting the novel's binary biographies of Conan Doyle and Edalji. "Mr Barnes was happy with the final script," says Clunes. "In fact, he was down here on set just a couple of days ago, tickled pink to see a book he wrote some time ago through completely different eyes."

Conan Doyle, the son of an Edinburgh alcoholic, studied and practised medicine before Sherlock Holmes made him the second most celebrated late-Victorian author after Rudyard Kipling, and, amazingly enough, there he is on YouTube. "It's much later in life, talking piffle," says Clunes of the grainy black-and-white clip. "But you can see the smile lines on his face, you can see that there's a warmth there; and the endless portraits he sat for, mainly photographic – quite a dandy. I enjoy his – I wouldn't like to say pomposity – but he's quite cocksure of himself, and with a touch of Toad of Toad Hall. He bought one of the first motor cars without ever having seen one.

"Also what's interesting to me is that he was an early celebrity," says Clunes. "I'm someone who gets called a celebrity just because I'm on the telly doing my job; and I'm quite curious about that because I have a theory that before the age of telly, the first celebrities were people in big houses, who were recognisable because their carriage were bigger than anyone else's, or whatever.

"Down where I live [in west Dorset] there are generations of people in big houses and quite often, if they're a bit alpha, they take me on. They try and put me down: 'Well, you won't like me… I never watch television.' I didn't ask what you watched…"

Clunes, Braitwaite and family have lived in the Dorset countryside for the past 17 years, having also acquired a herd of cattle, a flock of sheep and 13 Clydesdale horses. "That needs checking," says Clunes, in a voice that suggests he'd rather be doing nothing more than counting his horses. "We've always wanted a field; and then a farm came up for sale, and it seemed better to farm it ourselves. We have a stockman, but if I'm home, I'll help out."

Martin Clunes in 'Arthur & George' with co-star Charles Edwards (ITV/Neil Genower)

Is he maybe re-creating an idyllic childhood of his own? "No, no, I'm the son of a luvvie," he says, referring to his father Alec Clunes, an actor and theatrical manager who died when Martin was the eight. Clunes's own early struggles included supplementing acting income by modelling for Gilbert and George, until an encounter with Harry Enfield led him to taking the part of Gary in Simon Nye's consistently funny and popular Nineties sitcom Men Behaving Badly. Since 2004, the success of his GP fish-out-water series Doc Martin has meant spending six months of each year in Cornwall, and he will be rejoining the cast and crew in Port Isaac later this month. "Just as we think, 'Wouldn't it be nice to spend more time at home with the horses?' we keep getting these bloody things commissioned and have to go and make them. Poor us."

Such is the seemingly unquenchable thirst for anything to do with Sherlock Holmes – and the fact that Conan Doyle went on to investigate other real-life cases – follow-up series of Arthur & George are not out of the question. "The great thing about ITV is that it's very clear; if nobody watches it, then that's it," says Clunes, who at least does not have the Conan Doyle estate to worry about. "We're quite lucky that we only have Julian Barnes to please because the estate… I've got a feeling that there's a lawyer for the deerstalker and the pipe. The Sherlock Holmes brand is a copyright minefield, whereas Conan Doyle's life is in the public domain."

Although the BBC1 Sherlock series has introduced a whole new generation to the Holmesian canon, Clunes believes our fascination with the detective has never really waned. "It's ever current, isn't it? It never goes away," he says. My cousin Jeremy did OK with it."

"My cousin Jeremy" is the actor Jeremy Brett, star of ITV's 1980s adaptations of Conan Doyle's stories, and widely considered the greatest screen Sherlock Holmes – although the role is said to have played havoc with the bipolar actor's mental health. "He was ill at the time", says Clunes. "But while he was doing it [the ITV series] there was a support network. You hand yourself over to a schedule when you're an actor, you just get told where to go, what to put on and when to eat, and he was all right. It was when that went, and he was left to his own devices, that I think it got progressively harder."

Early in Clunes' career Brett apparently offered to pay for his young cousin to have plastic surgery, to have his ears pinned back. "It flitted through my mind and I thought, 'No, I'll be fine'," says Clunes, whose prominent auditory organs have become something of a trademark since the days of Men Behaving Badly. And on the subject of Simon Nye's sitcom, is there any chance of a reunion with cast members Caroline Quentin, Neil Morrissey and Leslie Ash? "Neil and I did a little sketch for Channel 4 for testicular cancer last year, which seemed a good use of us, but, no, I'm 53," he says. "We nearly did it 10 years ago but Caroline quite rightly said, 'But what if it was awful'."

'Arthur & George' begins on 2 March at 9pm on ITV