James Norton won hearts in War and Peace – now he's terrifying us as Happy Valley's psycho

It was a great call, in every sense. The relationship between Tommy Lee Royce and Sergeant Catherine Cawood (played by Sarah Lancashire) in series one of Happy Valley was not so much cat-and-mouse as tiger-and-shark – two immensely subtle and complicated characters closing in for the kill. We last saw Tommy scrunched like a foetus on the floor of a barge as an out-of-control Catherine kicked ten bells out of him, but we knew that the fight wasn’t over.

“It’s an even stranger dynamic between them this time,” promises Norton. Tommy’s in jail, he’s been there for 18 months; there’s only one face-to-face meeting, at a funeral, between him and Catherine in the whole series. But they’re still totally obsessed; for each of them everything is fuelled by, rotates around, the other.

There are clues, in the first episode, that Tommy has taken to religion in jail, but redemption, you suspect, really isn't his thing.

"We discussed how there are two options available to someone in Tommy's position," explains Norton, who with the help of a psychologist has researched the nature of psychopathology.

“Either he stays as we last encountered him, in vulnerable, abused-child mode, or he works out what he can control from jail, and how he’s going to do it. We see him training in order to get physically powerful, and we also know he’s spent hours and hours just lying on his bed, filling himself with hate for Catherine.”

Bulking up for the role turned out to be more interesting than expected. “I went to the gym for a month, and I didn’t drink for a month, and it’s weird how that changes you; you do feel this increased sense of control. It was important to me to have that physical side to Tommy, because he’s a very vain man, but it was also about experiencing that obsessive, almost OCD quality that intensive training brings.”

Norton, mercifully, is not a Method actor; off screen he is positively twinkly with easy, impeccable manners. "For me, acting is all about empathy. I know I’m not the first actor to say this, but I believe it’s vital; you have to somehow like the character, or at least understand why they act the way they do. With Tommy, I can’t stand ‘outside’ and be cynical or judgemental about him. In his head, every hit, every rape, is about survival. It’s the saddest thing, just heartbreaking, when you think that someone can think of the world as so hostile, can be so threatened by everyone and everything, that he can justify what he does in his own head.”

This level of emotional connection with a character, once accessed, is never quite lost.

“It wasn’t hard for me to get back into the on-screen relationship with Sarah, even though I don’t, in this series, have the privilege of acting so much with her. What’s really wonderful about these long-form TV series is that you’ve got all these memories in the bank. I had Tommy’s story with Catherine in my head, but there’s a form of physical memory, too. I had physically been in that situation with Sarah kicking the s**t out of me, or me smashing her face against a wall: horrible, horrible stuff, but really powerful, and the kind of thing you don’t forget.

“Those things are now imprinted on my mind, so for the second series it was a case of re-engaging with them. I was almost surprised how easy that was. Sarah and I were staying in the same hotel and, because our characters spend so much time thinking and talking about each other, there was this funny moment when we actually saw each other across the bar and it was like, ‘There you are!’

The new series also features a creepily compelling performance by Shirley Henderson as a woman romantically obsessed with Tommy’s “celebrity psychopath” status. “People create their own fantasies around figures like Tommy,” says Norton, with obvious discomfort. When series one was airing, he was disturbed to receive messages from young women on Twitter saying: “Take me to your cellar”.

“I read some case studies and it’s very common, this instinct to save these broken souls. I think maybe the women feel protected by the fact that the object of their obsession is behind bars, but it’s not that simple; with Tommy, you never know if this new relationship is genuine or simply manipulative. But people are drawn to darkness. The reason why we love things like Happy Valley is that we are obsessed by the extreme edges of life, and these people are the absolute extreme.”

Versatile hair and exceptional good looks notwithstanding, one suspects it’s this deep thoughtfulness that lands Norton the parts. The son of teachers, he was educated by Benedictine monks at Ampleforth College in Yorkshire, and went on to read theology at Fitzwilliam College, Cambridge. He came at theology, he explains, not so much from a “belief-based perspective”, but as a way of looking at the effects that belief systems have on the world. At Cambridge he was heavily involved with student drama and Rada seemed a reasonable next step

“A lot of actors share that hunger for understanding, and for living your life in an inquisitive way. I think my degree set me up for that.”

A key scene in Andrew Davies’s adaptation of the BBC’s War and Peace has Norton’s character, Prince Andrei Bolkonsky, communicating Tolstoy’s existential angst just by looking at a tree. “There’s pages and pages of this intellectual wrangling in the book,” he laughs. “I was a bit nervous that I would simply look inanimate. But I couldn’t be more delighted by the way the public has got behind the show.”

Norton’s range is remarkable in an industry that loves to pigeonhole (filming Happy Valley series one and Grantchester back to back, he had to wear a hat over his “vicar hair” in his final scenes as Tommy). He’s politely frustrated by the argument that acting in Britain has become the preserve of the posh.

“There’s two discussions to be had. One is that producers are afraid of taking risks on actors; they somehow forget that actors are there to transform – it’s kind of the point of what we do. When Happy Valley first came up, I was in South Africa. So I auditioned on tape and sent it off. Which turned out to be lucky, as they didn’t know that I didn’t usually speak in a Yorkshire accent. They probably realised once they did a bit of research, but they took the risk, and I will be forever grateful. So many actors aren’t allowed the opportunity to transform because people have so many preconceptions about them and make so many judgements about them, just on the way they speak.

“It’s also true that there’s a lot of period drama done here. Americans love it, we love it, and we’re good at it. Often in these dramas there’s a disproportionate amount of RP [received pronounciation] speakers, so it follows that if there’s a higher amount of period drama, there’s a higher amount of ‘well-spoken’ actors.

“It’s a real shame, though, when you get some- body like Eddie Redmayne, who is such a great ambassador for British drama – two Oscar nominations in two years, it’s extraordinary – and at least half the press cover- age on him is about the fact he went to Eton. What’s their point? Are they asking him to take that into account and maybe take his foot off the accelerator for a while?It’s ridiculous.”

Norton has just returned from LA, where he’s been doing publicity for War and Peace and the forthcoming second series of Grantchester. He’s delighted about the latter: “It was lovely going back into that world, and the show has matured a lot. Everyone loves the relationship between Sidney and Geordie [Robson Green], but in this series we start to threaten and thwart them, so it’s a really interesting change of direction.”

Neither is he minded to decamp to Hollywood just yet. “There were a few meetings about meetings,” he says vaguely, “and of course there are wonderful opportunities for actors out there, but there are wonderful jobs here, too. And I missed the rain."

He’s not entirely joking. He lists his chief recreation as “chatting”, but when Norton isn’t playing tennis or cycling round London (he moved recently to Peckham, south of the river), he takes to the hills.

“My sister gave me a book of really long hikes in the UK, and my resolution is to go on a long walk, on my own, with a tent, once a month or at least every two months. Otherwise I’d just be at the National Theatre watching another play. I think it’s really healthy to take your head as far out of the industry as possible; otherwise it can become all-consuming.”

For now, however, Norton’s head is firmly in Happy Valley. “It was such a joy to return. Not only for the chance to go deeper into Tommy’s twisted, fascinating mind, but also to see where [writer] Sally Wainwright was going to take the show. I can tell you, she hasn’t disappointed.”

Happy Valley returns tonight at 9pm on BBC1