That's what attracted him to Ian McEwan's Atonement, which he was offered just as he was completing Pride & Prejudice. "The fact that it was another period film and it involved a love story probably . . .

made the producers feel comfortable. But what made me want to do it was that it was about happy endings and what they are for, and about the fact that they're not an avoidance, they're an aspiration, a hope and a way of healing things."

Richard Eyre had dropped out as director because of other commitments. "We started all over again with the script, " says Wright.

"I felt I had to take ownership of it. Richard's version was a more linear structure so you didn't get the replaying of events from different perspectives and you didn't get the three parts. You had the first part in a big house on a hot summer's day in 1935 and then Dunkirk and St Thomas's Hospital. I thought that was a shame. One of the things I felt set the novel apart was its playing with structure, as with films like Magnolia or Traffic. If you take all that out, you're left with a fairly conventional girl falls in love with housekeeper's son, little sister is jealous and destroys him. As Noel Coward used to insist, the structure and the plot are inseparable. The structure is the plot and the plot is the structure. Life is messy and untidy and so our storytelling has to be if it's to be truthful."

Wright has sympathy for the little sister Briony, a fledgling writer with a vivid imagination, who catches Cecilia having sex with Robbie Turner in the library.

Three different actresses play her, young Carlow actress Saoirse Ronan . . . familiar from The Clinic and Proof . . . when she is 12, Romola Garai at 18 and Vanessa Redgrave in later life.

"She's very precise and has to have everything tidy because she thinks the world is confusing and difficult, " says Wright. "She writes stories to create order out of chaos because chaos confuses her. I think I'm quite like that. So if people call Briony a bitch, I take it very personally. I completely forgive Briony. Her compulsion is to make some kind of linear narrative out of her life and to find some kind of meaning in it. It's what storytelling is and what history is and certainly what religion is. Atonement is about whether it's possible to atone for the sins of your life. If there's one thing that runs through my TV work and hopefully my films it's that we're all constantly striving for something that's just beyond us. Personally I like the idea of a higher power but I don't think that higher power has my future written for me."

The characters in Atonement are victims of their time and place and class. "No one learns this more than Robbie Turner, " says Wright.

"He's a product of a grammarschool education. He thinks that it's always going to be there for him and that he'll always have the patronage of the Tallis family, and then he discovers how vulnerable he is. In a way he is the higher self.

He is goodness. He is an ideal, because he is the projection of Briony's imagination. . . James McAvoy had the ability to let himself be totally vulnerable. I kept saying to him, it's a very difficult thing to be, to be good."

He had cast Keira Knightley as the tomboy Elizabeth Bennet in Pride & Prejudice because she was the same age as the character. "We caught her at just the right moment. She was a girl and she was experiencing new things for the first time. She still had those cheeks of a girl. I don't think she could have done Cecilia then. But now she's developed and she's grown up and turned into a proper woman with all the strength that comes with that, so Atonement was just the right time for her."

In writing Atonement, Ian McEwan drew on his father's ordeal at the time of Dunkirk. Joe Wright found a similar empathy with his father. "He was 35 . . . my age . . . in 1941 and so I've always been interested in what he must have seen around him at that time.

He was too old to be called up, so he was a fireman in London during the Blitz. On another level, with Atonement I'm trying to get closer to that man." His father, a puppeteer who founded the Little Angel Theatre in Islington is now dead. "Maybe I'm still trying to impress him. It's quite a good thing to be trying to impress people who are never going to be able to be impressed, because then you'll never stop trying."

Atonement opens on Friday