Not that the creator of such sparky series as Making Out and The Riff- Raff Element minds. "The sheer output has been limited because of being a mother," she observes, "but the sheer material generated by being a mother more than compensates. I'm happy with the choices I've made. I've never felt I've been held back because I'm not a man."
That does not mean that it's all been plain sailing. "The female lot is tricky once children come into the picture," Horsfield muses. "You have to make choices that in general don't fall to men. They tend not to have the make the decision: `Do I have to give up work?'
"I've never really got back up to speed for at least six months after each baby, which I've come to conclude is entirely appropriate. But it has massive implications in terms of whatever job you're doing. Paula Milne, Kay Mellor and Lucy Gannon [other notable TV writers] have had children. It is no coincidence that they came into their own after their kids were over the baby stage. It's a huge part of the equation."
Horsfield works at home, a state of affairs which she admits has "massive drawbacks. I have to rush out if someone bursts into tears, but having children has made me disciplined about deadlines. I know the time available for work is between 11 and five. There is no choice about whether the inspiration comes - it just has to. The children know not to disturb me, but they do if it's an emergency, like when my nine-year-old came in the other week and said, `I've just put Teletext on and it says Eric Cantona might be leaving'." In the eyes of passionate Manchester United fan Horsfield, "that is an emergency".
The latest fruit of her discipline is Born to Run, a typically engaging family saga which occupies a desirable Sunday-night primetime slot on BBC1. It centres on the tussles between a father and son of the neanderthal persuasion (Keith Allen and Terence Rigby) and the long-suffering women in their lives (Billie Whitelaw, Marian McLoughlin and Linda Henry).
Like her previous successes, it is something of a rarity in modern television drama: a piece overflowing with chunky, positive roles for women. "I'm one of five sisters, and that has had a huge amount to do with it. Something I've always written about is the basic bond between women," she continues. "No matter how much the odds are against it, and how much they irritate each other and get up each other's noses, and how much the bonds have been stretched, nobody's ever run out on anyone. Dramatically, that's appealing to an audience. They want to see something stretched to breaking- point without breaking - it's reassuring. The relationship will survive, and we all like to see survivors."
The other common thread running through her work is the family, which the writer sees as a wonderful vehicle for drama. "There's something for everyone with a family," she argues. "When I was doing The Riff-Raff Element, I thought, `This is very eccentric'. But so many people said, `That's just like my dad or my sister-in-law'. There's always someone you can identify with."
As Horsfield works on a semi-autobiographical four-parter about three sisters growing up in Manchester during the 1960s, the only cloud on the horizon is the TV trend towards by-the-yard, formulaic drama and away from her more "authored" style of writing. "Things can be so ratings- led these days that a potentially good product might not be given a second chance," she sighs. "I hate it when TV executives say, `Let's make more of the vet-police-ambulance format because that's what people like'. It's so patronising. Pigeon-holing of any kind frustrates me. I hope there'll always be a place for my sort of drama."
Born to Run, tomorrow 9.35pm on BBC1Reuse content