At a party the other day someone asked me quite seriously what I thought about the Oscar chances for “my” film, An Education. Well, I said, equally seriously, Carey Mulligan (who plays me) seems a shoo-in for best-actress nomination, and there is also much talk of Alfred Molina (who plays my father) as best supporting actor. I think Rosamund Pike deserves a supporting nomination because she is absolutely hilarious in the film, but it’s a “well-known fact” that comedy never wins Oscars. And of course Nick Hornby deserves an Oscar for best film adaptation. All this uttered with convincing gravity, as if I actually knew what I was talking about. Since when did I become a film expert? How on earth did it happen?

I suppose it all began six years ago when I wrote about my schoolgirl affair with a conman, Simon, an associate of Peter Rachman, the notorious slum landlord. It was l960; I was 16, living with my parents in Twickenham, when this suave older man in a red Bristol sports car drew up beside me at a bus stop and offered me a lift home. For the next two years I led a strange double life — going to school and swotting for my A-levels during the week, then swanning off with Simon for weekends in Paris, Rome, Amsterdam.

What was extraordinary was that my parents let me — up till then they’d put all their energy into urging me, their only child, to win every possible scholarship and go to Oxford. But they were completely charmed, or conned, by Simon, to the point that they were putting pressure on me to marry him. I don’t want to give away the denouement but I escaped his clutches in the nick of time. I went to Oxford, he went to prison.

It was a story I always meant to write one day, but I thought it could wait till I was retired and my parents were dead. My parents always hated to be reminded of the Simon debacle — they felt even more betrayed by him than I did. But then my husband was diagnosed with myelofibrosis and told he had only two years to live unless he had a bone-marrow transplant. He was only 58, the same age as me, but suddenly death seemed just around the corner. I went up to my study and wrote the story in about two days flat. I have never written anything so easily before or since — it felt as though the story was already fully formed in my head and I just had to type it out.

I say story, and it felt like a story; I was writing it in a voice that was not quite my own. I think it was the voice of my 18-year-old self: there was an arrogance and sureness of tone the present me can only envy. How brilliant I thought I was then!

I published the story in Granta magazine because I didn’t want my parents to see it and knew that Nunton, Wilts, where they lived, was a Granta-free zone. Soon afterwards my agent rang to say a film producer called Amanda Posey wanted to meet me with a view to optioning the story. It was the worst possible timing — my husband was in hospital having his bone-marrow transplant and I was virtually living there — but she said she would come to a nearby coffee bar any time I could get away. She came with her co-producer, Finola Dwyer. They seemed bright enough, but not remotely like my notion of film producers, which involved fat cigars and vicuña overcoats. Amanda asked if I wanted to write the film script myself and seemed delighted when

I said no — she said she already had a screenwriter in mind. I thought she was mad and went back to the hospital and forgot about her. It was just one more weird incident in those weeks of constant weirdness that ended with my husband dying.

Among the many funeral bouquets was one “From Nick and Amanda”. Total blank. Some time later my agent explained that Amanda Posey was the girlfriend of Nick Hornby (she is now his wife), and he was the screenwriter she had in mind. He had spotted the story in Granta and showed it to Amanda, who showed it to Finola, who agreed it would make a good film. They kept batting names of possible screenwriters between them and Nick kept finding fault with them (“He was jealous!” says Amanda), till eventually he said: “Why don’t I do it?”

Nick seemed to know the characters way beyond what I’d said about them, and to intuit completely what it felt like to be a l6-year-old schoolgirl who was on the one hand very intelligent but on the other hand very ignorant about the world. He even seemed to understand my parents, which is more than I could ever say myself. He asked a lot about period detail: what posters I had on my bedroom wall, what music I listened to. For a ghastly moment I thought he might be planning a soundtrack full of l960s pop hits — that black hole compounded of Cliff Richard, Paul Anka, Liberace, Lonnie Donegan — but Nick said no, he wanted to know what

I and my schoolmates really listened to. So I told him the truth: that we were far too pretentious to listen to pop. We listened to jazz at Eel Pie Island and collected records by French chansonniers like Jacques Brel, Georges Brassens, Juliette Gréco. He evidently took this on board, because it’s reflected in the soundtrack of the film.

I put a clause in the contract that I should have the right to see and comment on (but not alter) every draft Nick wrote. And there were so many drafts over the years — I think eight in all. He fleshed out characters who had been no more than names before and created whole scenes that were not in my story at all. He made me a cellist in the school orchestra and took me to an auction where I bid for a painting by Burne-Jones. He showed a positively eerie understanding of my father, giving him long rants (“Money doesn’t grow on trees, you know”) that are so exactly like the sort of things he might say in real life that I still have to keep pinching myself to remember Nick Hornby has never actually met Dick Barber. The only bad thing he did was to change Simon’s name to David, which was my husband’s name, and I wish in retrospect I’d put up a fight.

While Nick was working on the script, Finola and Amanda were looking for the money to make it. They also started talking to directors and enlisted Beeban Kidron. She was on board for a year and half, and helped Nick develop the script, then she had to jump off-board because she had a prior long-standing commitment to direct Richard Neville’s autobiography, Hippie Hippie Shake, co-scripted by her husband, Lee Hall.

Explore Film

• Film Reviews

• Trailers

• DVD

• London Film Festival

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010