If you're reading this we're going to assume you know who Keira Knightley is. If you don't; she's an actress and you need a different hobby because apparently you're useless at this one.

For those that do, there's a good chance the name Sharman Macdonald will be slightly less familiar. She's a playwright who co-wrote the script to Alan Rickman's first and most recent directorial effort, 1997's The Winter Guest, with Rickman himself, based on her own play, and she's also Keira Knightley's mother.

And The Edge of Love, which co-stars Sienna Miller, Cillian Murphy and Matthew Rhys, marks the first time the pair have collaborated; Keira acting from her mother's screenplay. So when we got the chance to sit down one-on-one with Knightley in London recently - during promotion for her latest, Atonement, we couldn't resist finding out how things went on set.

"It's absolutely amazing; completely amazing," she told Rotten Tomatoes, "her work is something that I've grown up with; it's always been a part of everything in my life. To be able to perform it was completely, completely extraordinary. And fingers crossed it'll make a good film!"

We asked her if she'd felt added pressure with her mum looking over her shoulder. " No," she said, "her script was completely wonderful. You never know what's going to work; you can have the best script, the best director and the best cast and still, for some reason, it's just not going to gel. Hopefully this one has, I think she's done a tremendous job on the screenplay.

" And yes, I am biased, but really I wouldn't have done it if I'd have thought it was crap and, really, we've got a fighting chance of making a really good film and that's all anyone's got. You can't ask for more than that."

She was remaining cryptic on the plot, telling RT, "It's about a friendship group that implodes and a situation that leads to an act of violence," before catching our look and laughing as she said, "It'll make sense when you've seen the film!"

The film is directed by The Jacket helmer John Maybury, and will hit screens sometime next year. Meanwhile, Knightley can be seen in Atonement which opens this weekend in the UK and on December 7th in the US.

Be sure to read our full interview, in which Knightley talks to us about the film, right here. And you can catch our interview with her Atonement co-star James McAvoy over here for a little juice on his upcoming Wanted co-starring Angelina Jolie.