IT could hardly be colder, greyer or wetter in Hebden Bridge, but the weather doesn’t detract from the beauty of this sleepy market town nestled in the West Yorkshire valley of Calderdale.

Appearances can be deceiving though, as this is where Sally Wainwright, the Bafta-winning writer of Last Tango In Halifax, has based her new series, which doesn’t shy away from depicting the area’s drug problems or the potential for horrific crime within its idyllic surroundings.

At the story’s core is Catherine, a local sergeant who’s now raising her grandson following her daughter’s death eight years ago.

Wainwright’s made no secret of the fact she wrote the role with Sarah Lancashire, who’s been Bafta-nominated for her role in Last Tango, specifically in mind.

“It’s very flattering, but also with that comes a sense of responsibility, because she’ll have had expectations,” says Lancashire, who turns up to chat during a filming break in her character’s off-duty clothes, an arm encased in a fake sling.

Speaking cautiously with long pauses, she says she hopes people won’t play on the fact that it’s the same writer, same actress. “Yes, it’s not a coincidence that I happen to be doing another Sally piece, it’s lovely to be kept in the fold a little bit longer, but it’s very different from Last Tango,” she states.

The story begins with Catherine going about her daily business, until a flustered man (played by Benidorm’s Steve Pemberton) arrives at the local police station to report a crime, but loses his nerve before revealing what it is.

What Catherine doesn’t know is that the crime was his own brainchild — to kidnap his boss’ daughter and use the ransom to put his kids through private school.

He’s had second thoughts, but local drug kingpin Ashley (Joe Armstrong) has already put the plan into action and employed two young men to carry out the act. Even Ashley isn’t aware of the depravity capable of one of them, however, the psychopathic Tommy (James Norton), who Catherine has a complex history with.

“I read the first couple of episodes and there were hints of where the story was going to go, but it wasn’t until I’d read all six episodes that I realised how dark and tragic the piece is,” says 49-year-old Lancashire.

“It’s about a woman who’s very damaged by her experience of losing a daughter and put in a situation where she’s trying to get by day-by-day, and trying to find some inner peace.

“You realise she’s a bit messed up, like we all are, whether we like to admit it or not. I like that.”

Mother-of-three Lancashire understands how Catherine could carry on under such awful circumstances.

“I think we all do it actually, every day. That’s all we’re doing. We’re each just trying to get through life as best as we can, the only way we know how,” she says. “I admire the character. She doesn’t give in and she never will.”

As compassionate as she is, there are facets of Catherine’s character that are ugly at times. It’s something that Lancashire, who came to prominence as Raquel Watts in Coronation Street in the early Nineties, praises Wainwright for depicting.

“Sally’s never afraid to portray women’s flaws, which is great, because we’re all flawed. And she doesn’t necessarily make her women attractive, which is great too.”

Wainwright also directed one of the episodes, and the actress says she’s glad her friend was “terrified” by the prospect. “It’d be strange if she wasn’t, but I thought she was sensational because she knows her characters so well.”

After wrapping up the second series of Last Tango last year, Lancashire had five weeks to prepare for Happy Valley. She describes herself as “a fierce researcher” and learns her lines inside out.

“You have to get something in the bank before you start, otherwise you get into trouble,” she says.

She also shadowed the Calderdale police — only during the day though because, as she puts it, “things change” after dark.

The drama airs next week but it’s already getting positive feedback from previews, though it’s unlikely Lancashire will be tuning in.

She said: “I’m not very good at watching myself. I find it very difficult to distance myself from the process of filming.

“I’ll just look and go, ‘Oh God, why did they choose that take?’” she explains.

n Happy Valley begins on BBC One on Tuesday.