For one of Britain’s most successful actors, Sarah Lancashire is curiously uncomfortable in front of a camera. Here, in the bowels of the Piccadilly Theatre, she stares down the lens with girded poise. It’s eight years since she had to endure a photo session without having a character to hide behind, she explains in her soft Manchester accent. “I’ll just think of it like childbirth,” she mutters as the lens looms close, “you know the pain is eventually going to end.”

Is it actressy haughtiness that is making Lancashire itchy about punting herself? Actually it feels like the opposite. It’s the incongruity of selling a personality that, from her four years as the ditzy Raquel in Coronation Street to her abrasive investigator in ITV’s Rose and Maloney, she has invariably buried in her roles. In the nine years since leaving Corrie, she has appeared in enough 9pm dramas — Clocking Off, Seeing Red, Where The Heart Is — for people to talk about a Sarah Lancashire vehicle as a genre in itself. “Am I a brand?” she frets. “Does that bring responsibilities with it? Heavens.”

Her latest job, though, takes her into more showbizzy territory. In two weeks she plays her first night in Michael Grandage’s West End revival of the musical Guys and Dolls. She’s in the first cast change of a show that, with its current star Ewan McGregor, has been one of the cast-iron hits of a rusty year. The EastEnders old boy Nigel Harman replaces McGregor as the hustler Nathan Detroit. Lancashire, in her first stage role for 13 years, plays Nathan’s stripper girlfriend Miss Adelaide — replacing Ally McBeal's Jane Krakowski, who, according to the placards outside the theatre, “amazes with her utterly stunning singing and dancing”.

“So, no pressure there then,” deadpans Lancashire. She admits that the choreography has given her a few sleepless nights since rehearsals began last month. She keeps reminding herself that she’s an actress: “I can’t suddenly invent skills that aren’t there.” But she’s acted in musicals before — her West End debut was in Blood Brothers in 1990, just before she landed the Coronation Street job. Even so, when Grandage asked her to step into the role of Adelaide, Lancashire was so surprised that she found herself giving “a knee-jerk yes”.

But doesn’t this mean giving up lots of lucrative TV work? Apparently not. This year, she has done only eight weeks’ filming — on the second series of Rose and Maloney. Other than that she’s been spending time at her home in Richmond, southwest London, where she lives with her three sons, her second husband Peter and her mother Hilda.

If there’s a sense of her as never being off the television, that may come from the period between 2000 and 2002 when she had a lucrative “golden handcuffs” deal with ITV. During that time, she admits, she did “too much work”, not all of which was consistently good. Since she had her third child, Joseph, in March 2003, though, she’s been happy to wait, biding her time for work she really wants.

Even so, Lancashire is as surprised as anyone that she should be moving into musicals at the age of 41. It could well be astute casting on Grandage’s part. Adelaide is a role that calls for both comic brio and emotional tenderness — a combination that Sarah Lancashire could print at the top of her CV. It’s what made Raquel such a standout character; it’s what she brought to this year’s The Rotters’ Club, playing a restless housewife in 1970s Birmingham. Both offered ample temptation to sell the characters short to extract some laughs. But she is firm about seeking out the truth of her characters, she says. Growing up with a television scriptwriter for a father, she has an uncommonly strong affinity with the aims of the writer.

“My father was an absolute perfectionist to the point where it tortured him,” she says. “And the truth of what he was writing was something which mattered beyond anything. So I think I’m quite extreme in this, but I do have absolute respect for the writer. The least you can do, after they’ve sweated alone, is give it the respect it deserves.”

Geoffrey Lancashire died last year, aged 71, but his passion for the form that gave him his livelihood burns on in his daughter. She admits that it’s a medium much abused. But she’s also vehement that, in a country with no real film industry, it deserves more respect. “At its best, it’s sensational,” she says. “We should treasure it. We should protect it.” And the way she uses words, repeating and recasting phrases for emphasis, speaking with the clarity of a punchy script, suggests that she’s very much her father’s daughter.

Would she like to do more work behind the camera? So far she has directed one afternoon play for the BBC, Viva Las Blackpool, which won a Bafta nomination. “I was chuffed to bits by that,” she says, “because it was something I was desperate to do. And now I think the only ambition I have is to write a piece and direct it. And I say that very quickly because it’s not likely to happen.”

Why not? “Because I run away from it. Because I feel that writing is so revealing. It’s just so much more exposing than acting.”

Hmm. Could writing also be something that would put Lancashire up against her beloved father? She pauses. “My Dad always told me to write,” she says quietly. “But I couldn’t do it while he was alive. And maybe I could now. He was a very harsh critic. He was my harshest critic other than me.”

Harsh in a good way? “Absolutely. My Dad would phone within two minutes of something finishing being transmitted. He would phone and he wouldn’t even say hello, he would say: ‘Yup, you nailed that one, kid.’ Or he would say: ‘Not your finest hour.’ And I valued his opinion more than anyone else’s because he knew what he was talking about. I miss that now. I absolutely do miss that.”