Once asked whether, given the opportunity to live his life over again, he’d make any changes, Woody Allen replied that he’d do “everything exactly the same – with the exception of watching The Magus”. The film version of John Fowles’s novel has long been forgotten, but you know where Allen was coming from. How many times have you thought: “Loved the book, hated the film”?

The film industry has always been rapacious when it comes to plundering the bookshelves. When The Lord of the Rings, Harry Potter and Narnia can generate crossover franchises worth tens of billions, you can understand why. A large proportion of films spring from literary wells, making the shelves of Waterstone’s an important part of the cinematic process (see, in the past 12 months, Casino Royale, The Last King of Scotland, The Devil Wears Prada). That’s not to mention the fad for adapting comic books and the increasing use of magazine articles. For a film-maker, optioning a book provides a packaged story off the shelf, as it were, with material that has been road-tested. Get it right – Schindler’s List, The Silence of the Lambs, Jurassic Park – and the dividends are huge. Screw it up, however – The Da Vinci Code, say – and devotees will howl all the way to the bus stop (not that, in that case, it made a jot of difference to the box-office takings).

Next month comes the release of the film version of Atonement, Ian McEwan’s 2001 bestseller (more than 3m copies sold). Reworking the Booker-prize nominee, a novel tailored in McEwan’s usual intricate style, for the big screen would seem an ambitious undertaking. Defying easy description, its story of romance and redemption revolves around the blighted love affair, as the second world war looms, between two childhood friends, Robbie Turner, a scholarship boy, and Cecilia Tallis, a brittle, aristocratic beauty, the transgressor being Cecilia’s fabulistic younger sister, Briony.

Atonement comes fully stocked with those features that can present huge problems in transposition: three separate narratives; a time frame spanning 64 years; epic battle scenes (the BEF’s retreat across northern France in 1940); the detailed workings of a wartime London hospital; and the seemingly unfilmic central conceit of an author’s ability to atone for previous sins through the power of the pen. And all on a low budget, by Hollywood standards.

“There is a sort of theory that you should adapt badbooks because they always make more successful films,” says Atonement’s screenwriter, Christopher Hampton. “Don’t do masterpieces, because they’ll be disappointing. I don’t think that. If you take a really good book, then the potential is for a really good film. But you’ve got to get it right.” Hampton knows what he’s talking about. An Oscar-winner for the adaptation of his own play Dangerous Liaisons, he has, via screen translations of Graham Greene (The Honorary Consul) and Joseph Conrad (The Secret Agent), become Britain’s certified master of the form.

In the expert hands of the British director Joe Wright, who brought us the much-garlanded, muddy Pride & Prejudice in 2005, Hampton’s assertion seems to have been borne out. Atonement opens this month’s Venice film festival: at 35, Wright is the youngest director to have been accorded that honour. And the resultant sumptuous epic, which stars James McAvoy, Keira Knightley, Saoirse Ronan and Romola Garai (as Robbie, Cecilia and the two stages of Briony), is already receiving the sort of prerelease wows that propelled The English Patient – another skilful adaptation – to Oscar glory a decade ago.

“I’m dyslexic, right,” says Wright, crafting a roll-up in his noisy Soho production office. “I’d never read Pride and Prejudice. I’d never read any Ian McEwan. All my fictional education comes from film and television. I do find it weird that I’m taking on these great literary classics, but maybe that’s useful.” Clearly, it hasn’t been a disadvantage. Not the first choice to direct the film – which was Richard Eyre, who dropped out when shooting dates clashed with his commitment to do Notes on a Scandal, another literary adaptation – Wright inherited a script, worked up by Eyre and Hampton, that jarred with how he saw the film panning out. “They’d done away with the three-part structure. The points of view and Dunkirk and St Thomas’s Hospital were intercut, so it became a much more linear, traditional narrative. It diverged hugely from the book,” he remembers.

“I thought, ‘This is silly. If it ain’t broke, don’t fix it.’ And so what I did was return the script to the structure of the book, back to basics, which is exactly what I did with Pride & Prejudice. I don’t know how to make Ian McEwan’s work any better than it already is, and I would never presume to know.”

Hampton laughs and recalls: “He said what all screenwriters dread, ‘I thought the script was very good, but I’d really like to start from scratch.’ It had never happened to me before, but Joe had a clearly developed notion of what he wanted.” The pair holed up in a villa in Italy for a fortnight and rejigged the whole thing, going through page by page and finding a visual shorthand for what appeared in print. Hampton then departed to write a succession of drafts, McEwan gave periodic input and the process finally yielded a script to everyone’s satisfaction. “I was rather anxious about whether we’d done justice to him,” Hampton says, “because a number of his books have been filmed now [The Cement Garden, The Comfort of Strangers, The Innocent and Enduring Love], and a lot have been rather disappointing.”

Many things can sink a book-to-film conversion, such as bad casting and the sheer process of excising huge chunks of material. More often, failure can come down to the abstract notion of a two-hour movie simply not marrying with the images a reader has carried around for days, weeks, months. Wright thinks that is far too simplistic an assessment. “There are as many different versions of a book as there are people who read it, because it happens in your head. But in the same way, a film happens in your head when you watch it. Every audience member is seeing 24 still frames a second. There’s no such thing as a real film.”

Nonetheless, he and Hampton have certainly come up with a few ingenious solutions, not least regarding Robbie the soldier’s yomp to Dunkirk – here, more a solitary trek through the woods, rather than the streams of refugees and dive-bombing aircraft that McEwan’s bravura prose describes. “I was excited by the challenges of these great Stuka attacks and guns and bombs. I thought this was gonna be marvellous,” Wright chuckles. “But when we came to budgeting the film, it just didn’t work. I had a meeting with the producer, Tim Bevan [of Working Title], and said we needed extra money, and he said, ‘I won’t give you a penny over $30m to make an art film.’” Which is a pittance, compared with the average Hollywood project. Denied his Saving Private Ryan moment, Wright reserved his cast-of-thousands shot for the beach chaos of Dunkirk (actually Red-car), which he masterfully captures in one long tracking shot.

Crucially, too, Wright dismissed the notion of having the 13-year-old and 18-year-old versions of Briony Tallis played by the same actress (Vanessa Redgrave crops up as the elderly Briony in an imaginative reworking of the book’s conclusion). It might have been Keira Knightley as Briony, had the actress not lobbied instead to play the more emotionally fraught older sister, Cecilia, turning down several big offers for the chance to work with Wright again. It would seem no coincidence that Wright has drawn her two career-best performances out of her – he was vocal in his condemnation of Bafta, which snubbed Knightley for her Elizabeth Bennet in Pride & Prejudice, despite her Oscar nomination for the role. “I thought it was disgusting and still do,” he says. “She’s someone who’s had to learn her craft in public. She’s a far better actress now than she was when she was 15, but that’s hardly surprising.” She’s still only 21, he points out. “Her performances are subtle, intuitive and glorious when she’s given something to do. When she’s told to stand in the corner and look pretty... then I’dfreeze up.”

Casting was the least of Wright’s worries. Famously, the plot of the book hinges on a letter sent from one character to another that employs the anatomical use of the c-word. Wright recounts a meeting with a studio exec in Los Angeles at which the green-lighting of the movie rested on that one particular detail. “She said, ‘I have one problem. Couldn’t you use another word?’ And I said, ‘What word?’ She said, ‘The v-word.’ And I said, ‘What, vagina?’ It doesn’t have quite the Exocet missile quality that the c-word has. I said, ‘I’m sorry, I’m not willing to do that. We’re very excited about making this movie, but on one condition, and that is that the c*** stays in the picture.’”

Studio interference has done for many a film, of course. Alfred Hitchcock hated the meddling of the producer David O Selznick on his first Hollywood film, Rebecca, yet it is still hailed by Hampton as probably the best of all book-to-screen translations. “That’s a masterpiece in its own right. The film has some brilliant bits of invention in it that are even better than the novel.” He cites Mystic River as a great modern adaptation; Wright opts for Brokeback Mountain.

people such as Greene and Conrad and McEwan, it has to do with the creation of a world. Often, when you see an adaptation that isn’t successful, it seems that it’s just two people in a room – you just don’t get a sense of the ambience. And that’s one of the things Joe’s really good at.”

Once the cameras roll, it’s out of your hands anyway, Hampton says, and then there’s that “ohmigod” moment when you see your work on screen for the first time. When Dangerous Liaisons came out, he recalls, he had a meeting with the American screenwriter George Axelrod. “He said, ‘Are you pleased with it?’, and I said, ‘Yes, it’s absolutely exactly what I had in mind.’ And he said, ‘You’d better make the most of it, because it’ll never happen again.’ ” So what doesn’t work when it comes to translating words to the screen? Plays, it would seem, usually make poor films (exhibit A: The History Boys). In which case, Hampton’s Dangerous Liaisons would seem a rare exception. “I have a theory that plays and films are much less similar than novels and films,” he says. “Plays always have that artificial element. If you don’t somehow ruthlessly get rid of it, the film will somehow smell of the theatre.”

It’s perhaps with that thought in mind that Wright has eschewed a mooted third film version of the play Gaslight (currently at the Old Vic, starring his girlfriend, Rosamund Pike) and is pressing ahead with two other projects: a film about homelessness, set in LA, starring Jamie Foxx; and Perfect Wonder, about the West Indian immigrant experience in Britain. Hampton, meanwhile, is working on a script about Tokyo Rose with Frank Darabont and does not give up hope that a version of Conrad’s Nostromo he knocked up for the late David Lean may yet see the light of day; or his treatment of Donna Tartt’s The Secret History, which was last in the hands of Gwyneth Paltrow and Miramax. “It’s particularly frustrating,” he grumbles. “You know in your bones it would be a really good film.”

It may sound sacrilegious, but a film incarnation can actually end up becoming the standard. Pride and Prejudice, say, for all its literary reputation, is probably better known to most people from the versions seen on television or at the cinema. “I’m sure the majority of people who see films have not read the book,” Hampton concurs.

Will Atonement reach a greater audience on celluloid than in print? Vintage/Random House has, in traditional fashion, issued a reprint of the book featuring a still from the film on the cover, in anticipation of a further sales rush. “I mean, we’re not social workers, but in that sense it’s a positive spin-off of a successful movie, that hundreds of thousands of people read the book,” Hampton says. One would hope so, for it is, after all, an A-level set text.

“I hope they read the book, not just watch the film,” Wright says, “or they’ll fail.”

Writes and wrongs

Five films that transcend the literary original

The Godfather The director-for-hire Francis Ford Coppola turned Mario Puzo’s pulp novel into a film classic. Jaws Peter Benchley’s airport paperback was a big hit, but it didn’t have John Williams’s string section. Clueless Jane Austen’s Emma imaginatively reset in the demimonde of Beverly Hills teens. Perversely, it launched the Austen big-screen revival. Apocalypse Now Heart of Darkness as Vietnam war flick. Hands up who can quote Conrad? Now, how about “the smell of napalm in the morning”? Gone with the Wind Margaret Mitchell’s novel was a Pulitzer prize-winning bestseller, but the film has proved the enduring version.

And five that don’t Dune Frank Herbert’s galactic sci-fi epic rendered an incomprehensible mess by an apologetic David Lynch. Memoirs of a Geisha Arthur Golden’s meticulously researched work as Disneyfied, anglophone take on traditional Japanese culture. Award-winning kimonos. Captain Corelli’s Mandolin Ambitious, beautiful and unfairly brutalised, but fans of Louis de Bernières couldn’t forgive the filleting of large portions. The Bonfire of the Vanities The ultimate lit-flick clunker. Tom Wolfe’s hard-boiled take on 1980s corporate bastardy reborn as a comedy. . . with Tom Hanks. Inspired a tell-all book, The Devil’s Candy. Angela’s Ashes It looks right, smells right, but somehow just isn’t.

Atonement is released on September 7

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