Sarah Lancashire takes on another 'rare beast' in the third and final part of Jack Thorne's blame trilogy, The Accident. But she's not seeking out profane subject matters - rather it's the fearless writing that counts, she tells Gemma Dunn.

Sarah Lancashire isn't into labels.

Whether it's 'national treasure' or 'queen of gritty drama', the actress - hailed for her Bafta-winning performances in Last Tango In Halifax and Happy Valley - simply doesn't care for them.

"I just take what resonates really with me," she insists, chewing over her impressive body of work.

"I don't want to be the 'queen of gritty drama'. I don't. Gritty though it may be, these are pieces that say something about the world. That focus on the grey matter, that [aren't] black and white - as life is not black and white!" Lancashire, 55, protests.

"So I don't actively search out these roles," she reiterates. "I do the best of what comes along and that's really how I make my choices - and not a lot of humour comes my way!"

Not that it matters. For since her breakthrough as Corrie's lovable barmaid, Raquel Watts, the Oldham-born star - once named the highest paid actress on British television and the proud recipient of an OBE - has found critical acclaim with hits such as Where The Heart Is, Clocking Off, Lark Rise To Candleford and, most recently, MotherFatherSon.

Her next outing certainly isn't a laughing matter, either.

Lancashire will reunite with Kiri writer Jack Thorne for The Accident - a four-part drama series about a devastating explosion on the site of a large construction project in a fictional Welsh town, Glyngolau, and the fallout for the local community.

She will play Polly Bevan, the wife of the local politician who championed the project and the person to whom the stricken community turns following the disaster.

The third instalment of Thorne's Channel 4 'blame trilogy', the part was specifically written for Lancashire. And it was an offer that warranted an "easy yes".

"It's just the piece in its totality, really," she says of its appeal. "It's difficult to extract the character out of the scenario, so it's just the landscape of the story within that and the interaction of the characters.

"When it works, it's fantastic," she reasons, adding, "I feel very blessed that I receive pieces like [this].

"With most things Jack writes, it deliberately shines a light on that really difficult place where the public, political and private collide.

"I mean this in the nicest possible way, but Jack does this extraordinary thing where he takes a huge story and makes it tiny," she declares. "So, he does exactly the opposite of what most people do and then he distils it further and examines it forensically through the eyes of those who are most affected.

"His writing is extraordinary," she concludes. "It has something very bold and brave and fearless to say about the world that we live in."

Is that a rarity in the scripts she receives?

"The Jacks and the Sally Wainwrights are rare creatures; you're not going to find many of those around," she warns.

"But I guess, in the law of statistics, that's probably right?" she muses. "There's not going to be a huge number of great writers or a huge number of great directors, that's why they're unique and great, I suppose."

It's what makes this process a satisfying one, Lancashire follows: "It's the alchemy of having these extraordinary four scripts and having the right director for the piece in Sandra [Goldbacher], who just led us so brilliantly.

"And because of the nature of the piece as well, the nature of some of the scenes, it depends on an enormous amount of trust and respect within the space," she says. "And Sandra is a brilliant enabler; she makes the space very safe for you to work, and that's really rare.

"It was so rewarding in that respect and difficult to walk away from," she admits. "These experiences don't come along very often so you don't really want to leave them behind because you think, 'Well, that's another 10 years before one of these crops up again!'

"We all went away and decompressed. It was very intense," she recalls. "And that's the happiest place to be, when you are emotionally athletic and you can really start flexing muscles that you didn't even know you had or you'll see how far you can push it."

As for the tricky job of nailing the Welsh accent, "I did a lot of work on that!" she quips.

"It was really challenging. It was awful," confesses the mother of three, who made the choice to remain in character between takes. "In fact we started filming this in April and, just to give you an indication of how long it took me, I had my Christmas dinner speaking in a Welsh accent!

"Six months of Welshness!" she laughs. "[My family] is so used to it; that's the downside of living with an actor, really, that you live with their work as well. It's quite normal in my house."

Next, Lancashire will star as mother Margaret New in the forthcoming big screen adaptation of Everybody's Talking About Jamie, as well as reprising her role as much-loved headmistress Caroline when Last Tango In Halifax returns for a fourth season in 2020.

Does she reflect on her career, which has spanned more than three decades?

"Nope. I can't even remember yesterday," she answers candidly. "I haven't changed as an actor. I have evolved, probably, in the sense that I'm 35 years older than I was when I first started.

"But I think the most fortunate thing about the position that I'm in is that I'm offered better roles than I was offered 20 years ago," she concedes, though she says she is not as wildly busy as she appears on paper.

"It just looks like I am. I take a break all the time. Literally I take six, seven, eight months out, so I have massive down periods of time.

"But that's mostly just to get on with my other job - as a family person."

The Accident starts on Channel 4 on Thursday.