The movie of Atonement, based on the bestselling novel by Ian McEwan, is set for release next month. Already there is much speculation as to how close to the original it will be. McEwan, whose novels often make it to films (The Comfort of Strangers, The Cement Garden) will be trusting that the Oscar-winning writer Christopher Hampton (Dangerous Liaisons) and the director Joe Wright (Pride and Prejudice) will be faithful to a complex storyline spanning 64 years and three narrative threads. Can they pull it off?

I have a few doubts of my own about this, but before I start throwing stones perhaps I should install bulletproof panes in my own house. For when I tot up the number of feature films to my credit (or otherwise), I find that more than half of them have been adaptations of literary works.

The most obvious of these was Women in Love, adapted from the novel by D.H. Lawrence. The first draft’s script was by the talented Larry Kramer who, I think, would be the first to admit that it was a little more Larry than Lawrence. Suffice to say his final version was much closer to the original, with the proviso that in bringing a novel of several hundred pages to the screen something has to go.

This has nothing to do with integrity or its absence. It’s simply what Hollywood calls the B.F. Factor – “butt fatigue” being the maximum time that the buttocks can tolerate the springs of the average cinema seat. This currently holds at the two-hour mark (Women in Love has a B.F. Factor of 2 hours 6 minutes).

Furthermore, differences as to the best way to tell a story can be lobbed at the director and screenwriter from all quarters. In Women in Love we decided that, discretion being the better part of valour, perhaps we should relocate the nude wrestling scene from a cosy interior in a stately home to a moonlit meadow at night and close to a stream (into which our naked men could tumble, thus hiding a multitude of censorable sins).

But we reckoned without the opinion of one of the male leads – Oliver Reed, who hammered on my front door one night as I was sitting down to dine. “She says it’s not like that in the book,” he said, bursting into the room and nodding to a shadowy female figure behind him. “She says they wrestle in the dining room, not some tacky field in the moonlight."

“It would never pass the censor. Anyway, it’s implausible,” I said, as he moved towards me . . .

A couple of minutes later there was a knock on the door. It was nanny May, the faithful retainer from below stairs. “Did you call, Mr Russell?" she inquired as I dusted myself off and struggled to my feet. “Fine, thanks, May,” I gasped. “Mr Reed and I have just had a script conference.”

The rest is history. It’s easier if the director does the adaptation himself – or so I thought when I was commissioned to write a script for The Devils. Not only did I have at my disposal Aldous Huxley’s masterful novel The Devils of Loudun, but also John Whiting’s dynamic play The Devils. The script could hardly fail. And Warner Bros totally agreed – until they saw my finished film and tore it to ribbons. Sometimes you just can’t win – not even with something as innocuous as The Boy Friend, which the book-music-and-lyrics man Sandy Wilson lambasted. Maybe he found my version of his twee little seaside trifle just too rich for his taste, offering as it did a veritable banquet of Busby Berkeley delights.

But enough about me – what about the rest? Classics get baked into all kinds of different pies. A Midsummer Night’s Dream worked both as a dark medieval tale about the twilight zone by the Royal Shakespeare Company and as a fluffy bit of Hollywood confection with Calista Flockhart, Rupert Everett and Kevin Klein. The Taming of the Shrew worked with Richard Burton and Elizabeth Taylor, and as Kiss Me Kate, a musical with cod Shakespearean lingo (“I’ve come to wive it merrily in Padua”, rhyming with “What a cad-you-ah”).

David Lean’s black-and-white Great Expectations has kept pace with the book as a classic in its own right, but the modernised version with Ethan Hawke lumbers along like a bad day at the office. Toni Morrison’s novel Beloved can be the closest thing to ecstasy in prose, but was merely embarrassing on film. Even with a big budget and Tom Hanks as one of the leads, the film version of Tom Wolfe’s The Bonfire of the Vanities was the movie equivalent of roadkill.

There’s no formula and no guarantee. There are a million more ways an adaptation can go wrong than right. Where there’s poetry in the prose, the challenge is to translate it to moving images with emotional punch, delicacy, rhythm and revelation. On some occasions ( The Little Princess, House of Sand and Fog, To Kill a Mockingbird) the transition from novel to movie goes right because the director has a vision as powerful as the one that propelled the words on to the page.

At heart, the two forms, movie and book, are irreconcilable. A book we “hear”, listening to our own reading. A movie we “see”. The images must move, clash and climax. Translating sound into picture requires the director to cross-reference senses. When you get a film/novel such as Perfume (smell) or Chocolat (taste), the book is always going to outstrip the movie – until the film of the future gives us smell-and-taste simulation. On the other hand, when the story moves into altered states (such as Altered States), the movie has the advantage. Film can deliver a stunning visual in a tenth of a second – think The Lord of the Rings, The Exorcist, The Sixth Sense and The Butterfly Effect.

It’s all about touch, really. The filmgoer’s bottom line: do I like it? Does it feel good? Does it disturb? Can I crawl into the story and walk around? Is my butt numb?

Atonement is released on Sept 7

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