Imagination, fantasy and poetic licence were ingredients that made Peter Pan a classic. Now a Hollywood blockbuster, Finding Neverland, which focuses on its author, JM Barrie, has been accused of taking those same elements too far.

The movie stars American heart-throb Johnny Depp as Barrie, who was Scottish, and Kate Winslet as Sylvia Llewelyn Davies, whose sons inspired the characters of Peter Pan and the Lost Boys, first seen in 1904. Barrie, who never had children of his own, met the boys in Kensington Gardens in London and became their playmate, developing a curious attachment which contributed to the collapse of his marriage.

The characters in the film are based on real people, including American theatre impresario Charles Frohman, played by Dustin Hoffman, and Sir Arthur Conan Doyle, creator of Sherlock Holmes. Many biographical details are diligently researched, yet in several important respects the screenplay departs from the historical record.

When Barrie first meets Sylvia she is recently widowed, having lost her husband to cancer; in reality, Arthur Llewelyn Davies was still very much alive and, according to some accounts, suspicious of the man lavishing so much affection on his wife and children. The film portrays four Llewelyn Davies boys, when in truth there were five. Mary Hodgson, the boys' nanny whom one of them described as the most important person in their lives after the mother, does not appear at all.

The film's production company, Harvey Weinstein's Miramax, insists it is meant to be a 'fictional retelling' rather than a biopic, but descendants of the Llewelyn Davies family expressed disappointment. 'It's a pity they didn't stick to the facts,' said Lady (Tessa) Montgomery, 71, great-niece of Sylvia, whose death in 1910 left Barrie to care for the boys. Films have a habit of rewriting history. People rewrite even slightly the story or a character and often the family find it's not the person they remember or know about.'

Lady Montgomery, whose father-in-law was Field Marshal Bernard Montgomery, also objected to the portrayal of her great-grandmother, Emma du Maurier. Played by Julie Christie as a steely matriarch, du Maurier spends much of the film bullying Sylvia, and trying to keep Barrie away from the boys, before finally melting. Told about the representation, Lady Montgomery, who has not yet seen the film, said: 'Judging by the letters to her from her son, Gerald du Maurier, she sounds a very affectionate and kind mother, so that's rather hard.

In one scene, when she is angrily waving a coat hanger, du Maurier becomes the source of Barrie's inspiration for the evil Captain Hook. 'I do think that's really rather ridiculous,' Lady Montgomery added. 'She might well be spinning in her grave.'

Kits Browning, 63, brother of Lady Montgomery - their mother was the novelist Daphne du Maurier - also raised concerns: 'In the 1970s Ian Holm played Barrie in a BBC series, The Lost Boys, by Andrew Birkin. He was somebody who would stick to the facts. It's very different when you get somebody in America who knows nothing about the family and is simply commissioned to write a screenplay. They don't care what happens so long as it puts bums on seats. They can shoot anything that is commercial and appeals to the American cinema audience, which is basically 15 to 30.'

Browning, himself a film maker who now runs the annual Du Maurier festival, added: 'With a lot of these things, once they're taken over by a film company, you just have no control at all.'

Beryl Bainbridge, whose novel An Awfully Big Adventure was partly inspired by Peter Pan , condemned Finding Neverland. 'If you're going to do "the life of", you can have your own ideas but you can't alter facts.'

The film's screenwriter, David Magee, whose credits include the action adventure Crisis Four , defended his approach: 'The screenplay I wrote is not a factual retelling of what happened to James Barrie when he wrote Peter Pan. I wanted to tell a story about what it means to grow up and become responsible for those around you.

'We made it so the boys' father died before the film starts because we thought having two horrible things happen to these children would be too much in a two-hour time frame. The character of Emma du Maurier totally has my sympathy and I hope she is beautifully redeemed in the end scenes. I never intended any character to be a villain in any way.

'It's a creative fantasy about children who grow up too quickly and a man who hasn't been able to grow up. I hope JM Barrie would respect what we tried to do.'