'˜As powerful as the first series' - James Norton

The downbeat drama, written by Last Tango In Halifax’s Sally Wainwright, sees the 30-year-old reprise his role as psychotic Tommy Lee Royce.

Set in Calderdale, it stars Sarah Lancashire as Royce’s nemesis, police sergeant Catherine Cawood.

Happy Valley captured the imagination of viewers, drawing an impressive consolidated audience of 7.8 million for its series one finale in 2014.

“The last series, we were the underdog, we had everything to prove so nothing to lose,” said Norton.

“But now, with the success of the first series, of course there’s that inevitable second series fear.”

Scriptwriter Wainwright, who is originally from Calderdale where the award-winning BBC drama was filmed, had to convince Last Tango In Halifax’s Lancashire to return, and fans hope Happy Valley will avoid the mixed reaction that greeted series two of ITV’s Broadchuch.

“Sally’s such a talented writer. I think she’s taken intentional steps to make it a slightly different feel, different structure,” Norton said.

He added: “It’s as good. I think it’s as powerful, if not better. That’s why I wanted to be in more of it.”

The London-born actor had not expected to play a part in the follow-up because the first instament ended with the police apprehending his character Royce for kidnap and murder.

“I was surprised. I must’ve been one of the last to get the call,” he said. “There wasn’t any guarantee I’d be there.”

Dedicated and professional in her job, Cawood’s personal life is littered with family tragedies: she believes Royce is responsible for her daughter’s rape and eventual suicide.

Grandson Ryan (Rhys Connah) was conceived as a result of the assault.

The policewoman has a broken marriage and an estranged son.

Her sister Clare (Downton Abbey’s Siobhan Finneran) was in recovery from heroin addiction, but has fallen off the wagon.

As the second series of Happy Valley got under way this week, a bare-headed Royce is in jail.

“I’ve never shaved my head before,” Norton admitted.

“We talked a lot about how we wanted to present him 18 months on from the first series. I think that for someone like Tommy going into prison, he has two choices: either collapse and be destroyed by it or confront it and take control. We decided that obviously Tommy would do the latter.”

The dynamic between Cawood and Royce was a highlight in 2014, but series two will see the unhinged man find a pen pal played by Harry Potter actress Shirley Henderson.

“It starts with a letter and then friendship and starts to become this very bizarre relationship,” the War And Peace actor revealed.

“It’s been a wonderful relationship to explore with Shirley Henderson, who’s amazing.”

He added: “Any time there’s any sense of hope for Tommy, it’s always taken away from him.

“He does love his son. But it’s always about Catherine because, in his head, she’s the person who put him in prison,” Norton said.

The first bleak series contained disturbing scenes, in particular a bloody fight between Cawood and Royce which sparked some complaints to media watchdog Ofcom.

“There are bits of violence in it again,” the Yorkshire-raised star said. “Catherine’s a copper in Halifax and the great thing about Happy Valley is the setting.”

He added: “Parts of the north are grim ... it’s grim up north.”