Sally Wainwright: not the same old

^'I've never had feedback like that before," says writer Sally Wainwright of the correspondence she received last year in the wake of her BBC drama Last Tango in Halifax, about two septuagenarian sweethearts. "As a writer, you don't get many letters from members of the public. I think I've had the same number for Last Tango that I've had in the past 20 years." She adds, drily: "That's about seven."

Last Tango, which won two Baftas, returns for a second series this month. It is popular, in part, because it tells the story of older people without depicting them as senile or terminally ill. Actors Derek Jacobi and Anne Reid, who play the couple, report receiving an "extraordinary" public thumbs up.

"It's so un-ageist," says Reid. "I get scripts all the time that say: 'This old lady comes in on a zimmer frame.' And I think: 'Oh hello, that's my part, is it?' No, thank you. Lots of people in their 60s and 70s are not doddery old idiots, and [they] are having interesting lives."

If you typified Wainwright's work, you'd pick out her flawed but sympathetic characters, her sense of humour and her pithy social observations – underpinned, she hopes, by a "ripping yarn". Despite her track record – At Home With the Braithwaites, Unforgiven, Scott & Bailey – the BBC and ITV turned down Last Tango when she first pitched the idea, the suspicion being that senior citizens were considered a viewer turn-off. Wainwright says she never really found out why. "You're at the whim of whatever the trends are. You go away and swear a lot because you feel passionate about it, but it's part of the job." Six months later, having presumably woken up to the maturity of its audience, the BBC changed its mind.

Last Tango was never conceived as a retort to an imbalance in the demographic reach of television: it was essentially a story about her widowed mother, who, at the age of 75, fell in love with a man she'd known at junior school. "It was about dramatising how mum became a different person," Wainwright reflects. "I wanted to show them going out and having fun, because that's true to what happened. My mum came to live with us when my dad died. Then she just took off."

Was she shocked? "I was a bit surprised. She was worried that everybody would think they were silly old beggars. But I thought it was great. Then she said they were going to get married, and I was like: 'Wow!'"

Like her other dramas, Last Tango has more up its sleeve. If the seventysomethings are prominent, so are their dysfunctional families, particularly the daughters: one a snooty headteacher who has recently come out as gay, the other a sheep farmer surrounded by the fall-out from several messed-up relationships.

With downbeat drama dominating TV schedules, Wainwright points to the uplifting nature of the plot as part of the show's appeal. "What was different about this was that it offered people hope. So many series lately, like Broadchurch and Southcliffe, seem grim and not much else. I need something lighter. Real life is a mixture of dark and funny. I persevered with Top of the Lake [the recent Jane Campion miniseries] for four episodes, then I was ready to slit my wrists."

Wainwright's taste for strong female characters also distinguishes her writing. She shrugs as she recalls someone claiming, at an industry conference, that viewers prefer powerful men. "I'm rare in that I like to see women in strong roles. The shows I liked [growing up] were about strong women: Juliet Bravo, The Duchess of Duke Street, Rock Follies." How about the accusation that the men she writes are weak? "I don't think so. I just don't focus on them. I resent it because there's this perception that I consciously write men as twats. I don't."

Last Tango isn't the only script on her plate. Scott & Bailey has now being picked up for a fourth series. Its genesis was less personal: Suranne Jones, star of Unforgiven, fancied doing a British Cagney & Lacey, and Wainwright was brought in to fashion the plots. But she found a way in via long conversations with a Manchester detective inspector, Diane Taylor. "I couldn't have invented the stuff that she told me, like interview techniques, which we've seen dramatised so many times – wrongly. We did it as accurately as we could, where it's very calm, very planned."

Police work also features in her new six-part BBC1 series Happy Valley, which begins filming later this month. It stars Sarah Lancashire as a West Yorkshire police officer grappling with a mysterious kidnapping, and is described by Wainwright as "Juliet Bravo meets Fargo". Then there's a new biopic about the Brontë sisters, again for the BBC. "I'm fascinated by three literary geniuses in one family, and the fact that they had such robust imaginative worlds inside their heads but outwardly they were regarded as mice."

Wainwright is big on authenticity. It's no accident that mid-life rethinks loom large in her work, she says. "Middle age is an interesting period to write about. You've got teenage children to deal with, elderly parents. You're at the peak of your career, so you've got a lot of responsibility, pressure, people waiting for you to make decisions. It's fulfilling on one level. On another, you feel you're only just getting by. I do [feel like that] most days."

I wonder how her mother felt about Last Tango; did she have any qualms about being depicted on screen? She laughs, and admits she jibbed a little at a scene where her on-screen counterpart regards her daughter's gay partner with obvious distaste.

"I tried to explain that you've got to have some drama in it, that it's not all about her," Wainwright says, and smiles. "She does read the Daily Mail, though."