Play it by the book: One Day shows that bestsellers don't make great films

The disappointment was palpable in the ladies' toilets. Straight after an early screening of One Day, the new film adapted from the bestselling book of the same name, women were moaning over the stalls to each other.

"Her accent was awful," lamented one voice.

"It just... wasn't as good as the book, was it?" the other called back.

This is a typical reaction when a bestseller is made into a film and you can expect to hear more of this whining after One Day is released in cinemas today. Hopes for this film are high; people care about this film a lot. And people care about this film so much because they care about the book: it is some time since a novel resonated with the British public as strongly as One Day.

Published in 2009, David Nicholls' love story begins on 15 July 1988. We meet Emma and Dexter on the day they graduate from university; the novel then checks up on them every 15 July for the next 20 years. Sometimes they are friends, other times they are not speaking, but the "will they won't they" aspect drives the plot forward and we are constantly kept guessing as to whether this vastly different pair will end up together.

After being published without much fanfare, to decent but far from overwhelming reviews, One Day became a word of mouth success. It has sold more than a million copies, been translated into 31 languages and spent three months on the New York Times bestseller list. It was the highest selling British novel of 2010. Seeing its celluloid potential, Nicholls (who has written episodes of the television drama Cold Feet as well as adapting another of his novels, Starter For Ten, for the big screen) began work on a screenplay soon after the book was published.

That is where the trouble starts. When it is announced that a much-loved novel is going to be made into a film, ardent admirers of the book become extremely nervous. Who will play their beloved characters? Will the film-makers capture the spirit of the novel? Can the film possibly be as good as the book?

I may not have been the biggest fan of One Day – finding it little more than a throwaway beach read – but many people have taken the novel to heart and they have been rooting for the film. So if the film turns out to be merely mediocre (which it has), they will feel let down. This happens almost every time a popular book is adapted. Have people not learnt by now? And why do people care so much?

If your favourite book is made into a lousy film, it doesn't change the book. Whingeing and moaning is futile. Of course a film is going to be different to a book – they are entirely different art forms. Sure, there have been some outstanding literary adaptations – from To Kill A Mockingbird to The Lord of the Rings trilogy – but I don't understand why people care so much when a favourite book fails to translate to inspiring cinema.

It seems to be a certain type of book that inspires this reaction. When a film presents an adaptation of a classic novel, yet another Dickens, Austen or Brontë, no-one seems to get too worked up. It is modern British hits that produce this hysterical response. Some of the biggest bestsellers of recent years – The Beach, Captain Corelli's Mandolin, Bridget Jones's Diary and Atonement – were adapted to varying degrees of success. All the films were heavily scrutinised, from casting through to release. Who can forget the stink caused after it was announced that a gaunt American, Renée Zellweger, was going to be playing the Ben & Jerry's-loving Bridget Jones? Predictably enough, the first complaints about One Day were heard at the casting stage. Jim Sturgess, who was chosen to play Dexter, escaped relatively unscathed, purely because no-one knew who he was. Casting unknowns in prominent roles is a shrewd move – they come free of baggage and without any major characters to be disassociated from. However, poor Anne Hathaway didn't escape quite so lightly when it was announced that she was to play Emma.

How was a beautiful American movie star going to portray a somewhat dowdy lass from Yorkshire? Well, by acting, presumably. But still, fans of the book were outraged. (To be fair, they may have had a point – Hathaway's accent is appalling.)

The film's director, Lone Scherfig, understood the conundrum she was caught in, telling New York magazine earlier this year: "No matter who we cast, someone would think that they knew who could play Emma Morley better. That's always the case when you work with something as loved as this book."

It just seems absurd to compare two such different art forms and feel so let down when a literary adaptation doesn't meet your expectations. In an interview, the French New Wave director François Truffaut asked Alfred Hitchcock if he would ever consider trying to adapt Dostoevsky's Crime and Punishment for the big screen.

"Well, in Dostoevsky's novel there are many, many words and all of them have a function," Hitchcock replied. "And to convey that in cinematic terms, substituting the language of the cinema for the written word, one would have to make a six- to 10-hour film. Otherwise it won't be any good."

While I am in no way suggesting that One Day should be considered as complex a masterpiece as Crime and Punishment, Hitchcock had the right idea about seeing literature and film as two very different disciplines that should be considered separately.

Any 90-minute film which attempts to recreate a work of fiction is going to struggle, something Scherfig is quick to point out: "Something will always be lost when you go from a book to a script, but I hope to give it something else that makes up for it. It is about turning [a story] into cinema."

Yes, it is possible to make a great adaptation. But before you buy your cinema ticket, just remember that if a film fails to do justice to your favourite book, it doesn't matter. Calm down and stop moaning. It won't change the connection you had with the book. What you loved about it is still there.

The words remain the same.