‘You can interview him, but you’ll have to do it while he’s fishing,” an ITV PR girl tells me. So I obediently follow the famous Fox son across the fields to the river behind the Oxford ice rink, where he stands, casts his line and waits for a fish.

“Caught much?” I venture, trying not to stare too obviously at heart-throb Laurence Fox.

“The odd perch, but I come here to get away really from the film unit and have a break,” he tells me, that long, thoughtful face uneasy with the publicity.

“It’s not good to sit inside all day so I come fishing, even though the others take the mickey constantly.”

But then he’s a fascinating character, old Laurence. As famous for his parentage and marriage, as his impressive acting career, the 31-year-old graces the celebrity magazines on a regular basis, while never venturing out, an unwilling paparazzi favourite.

On screen is about the only time you get to see him in the flesh, when his mysterious Lewis character, DS Hathaway, seems to ignite most of the female population. Lucky Billie Piper. Yet mention his ardent fan base and he almost winces.

“You’re just being flattering, very flattering. And we get to work with some amazing actors because the quality now is so consistent, and this year is the best so far for Lewis. But I don’t watch myself on TV and I make sure I’m busy on Sunday nights now,” he smiles, changing the subject brilliantly.

Laurence is protective not only of his own private life, but also that of his character James Hathaway. Which is why he is rather put out about the new series of Lewis, starting on Sunday night, when Hathaway’s character is brutally exposed. “Yes I was cross when I read the script because it’s all about Hathaway and I think the less you know about him the better and the more enigmatic he is, which is his secret. So I am possessive about him, not that anyone would ever listen to me,” he says with a wry grin.

“And I don’t like Hathaway’s car while we’re on the subject, and they could drop his love of ‘world music’,” he laughs, on a roll now, “but I do try to channel as much of the wardrobe budget my way as possible,” he grins.

It is this cheeky characteristic that makes Laurence so engaging. He plays up to his reputation, while Kevin Whately as Lewis is the daddy on and off screen. So what of their relationship? “It’s not too dissimilar to Lewis,” Laurence admits.” I annoy him and he forgives me. Kevin is the boss, though.”

Any good plots then? “Well I have a love interest that isn’t a murderous trans-sexual,” he grins again. “So things are looking up.”

Of course, filming Lewis takes up only six months of the year, and Laurence is obviously blissfully happy at home with actress wife Billie Piper and their son Winston who “sleeps very well”. As for coping with his newfound fame, Laurence jokes: “I only get mobbed in old people’s homes. And anyway people who do court publicity always get bitten in the arse.”

Despite his acting heritage (his father is the actor James Fox. Edward Fox, Robert Fox and Daniel Chatto are all uncles, Emilia Fox is a cousin) Laurence didn’t fall into the family business by any means.

Having been expelled from Harrow, he worked as a landscape gardener for a while.

“I was quite directionless,” Laurence admits, before his father suggested gently at breakfast one day that he might consider acting as an option.

Rada followed, as did his first film Gosford Park, and a part in The Last Drop, in which he was spotted by Whately who suggested him as a contender for Hathaway. So how much was Laurence told about his character in Lewis before he began the role?

“They just leave it up to you. They prefer us to make our own choices. But I still believe that the less you know the more you care, which keeps it interesting. I mean you didn’t know anything about Morse.

“I do love doing Lewis, though, and lots of people watch it which makes it all worth it, so I hope I’ve done it justice.” And with that Laurence Fox reels in his line and walks back to the film set, leaving me dangling just like one of his fish.

  • Lewis starts on ITV1 on Sunday night.