Longford's other lady

Duncan, who is in remarkable condition for her 55 years, was 15 when Hindley and Brady were brought to trial in April 1966. Tonight's film is interspersed with archive footage from the news programmes of the time. Shots of policemen and local volunteers combing the moors for children's bodies chill even now. Indeed the Moors Murders remain an iconic, defining event in British 20thcentury history, and resonate with generations not even born at the time - perhaps more than do the equally hor-"We'll never ever be able to erase that image, the Hindley photograph, from the national psyche," says Duncan. "The point is made by Elizabeth Longford in the film that Hindley was judged much more harshly because she was a woman. There is something about this young blonde woman, with the challenging expression, and the whiff of sex about her. But there was also something about that time, the mid-Sixties, which seemed to be on the cusp of the end of innocence, whatever innocence is. The fact that this man and woman had made a terrible pact, that men and women are supposed to raise children, not kill them.

"I think it was made more potent by its location too. We know about the moors

from the Brontës, they are literally part of our landscape and our history, woven through our literature. And then you think that children's bodies are lying beneath them. Nobody could write anything so dramatic. When I heard about this private screening for the families of the victims, it brought it home to me that for them, this goes on and on and on. It never stops."

Duncan, last seen as the voluptuous mother to Brutus in HBO's serial Rome, but perhaps best known, still, for the Marquise de Merteuil in Christopher Hampton's Les Liaisons Dangereuses, brings a quiet authority to Elizabeth Longford. She was part of that golden Eighties generation at the RSC, in a company that included Fiona Shaw, Juliet Stevenson and Alan Rickman, and despite a memorably bitchy performance as the powerful Barbara Douglas in Alan Bleasdale's GBH, alongside Robert Lindsay, her career has largely unfolded in the theatre rather than on-screen - Maggie in the National Theatre's Cat on a Hot Tin Roof in 1988 was a highlight.

She lives in Hampstead with her husband, Scottish actor Hilton McRae ( Duncan is herself Scottish, though she doesn't sound it), and their son Cal, 15. Ironically, given the plaudits recently won by Helen Mirren for work with both writer and director of Longford, Richard Eyre once described Duncan as "one of the top actresses of her generation, easily as good as Helen Mirren", adding that she wasn't very good at "self-promotion"-and implying that her career had suffered for it.

Duncan certainly comes across as a modest and very thoughtful woman. Theatre, she says, is important to her. For her next role, she is hoping to appear in a revival of Harold Pinter's Old Times in New York. "But we don't have a theatre yet. We've got everything else, just no theatre. I'm really trying to do a play, though. It's been a very long time." It's been four years, in fact, since a starring role in Noël Coward's Private Lives won her an Olivier Award in London and a Tony award on Broadway.

But first, she must weather the storm that Longford is bound to create. For the first time in her career, she says that she will take an interest in the reviews. "I've made a habit of never reading reviews, which is really something that comes from the theatre. You have to keep performing night after night and it's only ever the negative comments that stick in your mind, so I just decided it wasn't worth it.

"But with this, I think I'll drop the habit. I'll be very interested to see what the reactions are. I think it contains lots of questions that are worth asking: about our desire for vengeance, about the value, and cost, of religious faith and about how we treat people in prison. But, no, I won't be surprised if some of those reactions are really quite strong."

Longford is on Channel 4 at 9pm.