EVERY HISTORICAL FICTION or drama is the author's own recipe of three key ingredients. The mixture is always the same: historical research (anything from a pinch to a peck) the writer's prejudices and opinions (conscious and murkily unconscious) and the conventions of the genre. I have just had the thought-provoking experience of seeing my historical fiction, The Other Boleyn Girl, be adapted into someone else's historical drama and it has persuaded me to think about history, novels and film - their progenitors and ownership.

The historical research is a difficult quantity, since it is no more an objective account of the past than the novel that will be based, unsteadily, on it. It is no coincidence that our prejudiced opinions of women of the Tudor court are drawn from the devoted Victorian historians who were the first translators and publishers of original Tudor documents, but were deeply committed to their own view of women as either saints or whores. From them comes our still-held but most unlikely thesis that Catherine of Aragon was incapable of telling a lie, and our prejudiced view of Catherine Howard as a schoolgirl slut.

Even a history reflects the prejudices of its author.

At least with a novel the readers know that they are getting authorial interpretation. My own Tudor novels, starting with The Other Boleyn Girl, balance history and fiction. The research for the novel takes nearly twice as long as writing it, and it forms the backbone and the structure of the story. The historical account is the story of the novel and the fiction is the emotion, the motivation, the explanation for the historical facts. My Tudor books are specifically set in a place and a time, and that is accurate to the historical record when that is available. Sometimes, I can base a scene in the novel almost exactly on an account by a contemporary eye-witness. I took great pleasure in the colour of Mary Boleyn's dress at a masque since I had seen the accounts from the royal wardrobe that told me she was wearing green. The joy of this is an utterly private one.

Other writers are not so rooted in the historical record and their novels or dramas are more approximate. I put down Judith Paris by Hugh Walpole and never picked it up again, as his heroine escaped imprisonment by climbing down a drainpipe, years before the installation of indoor toilets or washbasins. We see the contrast between historical fiction and ahistorical romance in some interesting authors who wrote both. Georgette Heyer's Regency novels are set in a generic past, generally, post-Austen England, influenced by her own middle-class life in postwar England, and by her meticulous research. I found them utterly addictive. But her historical fictions, such as The Infamous Army and The Spanish Bride, are solidly based on the historical military records of the Battle of Waterloo and the Peninsula War, and can be found in the library at Sandhurst. She herself thought that the historical works were far superior to her romances, which she considered rather silly.

But even a story researched from history and recounted as accurately as the novelist can manage is going to be a vehicle for the writer's unconscious prejudices and conventions. Anya Seton's heroines have an affection for their children and a loyalty to their husbands that is pure 1950s. Heyer's romantic heroes are innocent of alcoholism or the abuse of working women. Walter Scott knowingly created the tartan myth, invented an entire national history and managed to sell the idea of ancient North Britain to the English reader.

My own interest in women's history and my aversion to English snobbery led me to write The Other Boleyn Girl as a triumph of the common sense of Mary Boleyn over the ambition of her sister Anne. If I had been a Victorian novelist, or even one of the postwar English novelists I would probably have written the novel from the point of view of the girl who would be queen.

I certainly would have written an account which suggested that Mary Boleyn's marriage, adultery and then second marriage to a third sexual partner must cast a slur on her reputation as a good woman, as a “lady”. Most likely if I had been writing in my mother's generation, I would have written her either as a victim of male sexual predation, or as a whore.

The idea that a woman could be sexually experienced and not a “bad” woman is a modern one. While it is true to say that until I recovered the story of Mary Boleyn from the footnotes of the history books no one had seen the potential of her story, it is also true to say that she could only be a heroine to a feminist, radical historian.

My novel can plough its own furrow. It has only one producer, one writer, one director and one actor: all me. If the book is not bought and read because it offends traditional readers, it will only be me out of work. In the novel I have hundreds of pages to develop my view and persuade the reader of my version of the characters. We follow Mary as she slowly realises that there is an interesting life to be had outside the glittering circle of the court, and this is both her realisation and also a revelation to the reader.

My unconventional take on the story does not fully translate to film. Historical drama can explain only so much. The medium of film traditionally shows the actions and the reaction of the characters. Even though the script sets out to adapt my novel as closely as possible, the film has to focus on the personalities of the two Boleyn girls, and their love affairs with the King. It makes the emotions of the women the centre and the driving force of the action.

Film is wonderful at conveying and evoking emotion, but books are better for ideas and evoking thought. And films, especially those with a huge budget, are bound to favour a conventional and popular view. It is assumed that the court of the king is of more interest than the house of the commoner, and undoubtedly it is a more beautiful setting. The combination of the snobbery of the audience, their love of celebrity and the glamour of the court is something brilliantly served by a film about handsome and sexually active royals.

The great drama at the heart of my novel is the competition between Mary Boleyn and her sister Anne for the attention of the King, and Anne Boleyn's pyrrhic victory which would win her the crown but lose her her head. The film emphasises this superbly, and the actors are riveting and beautiful. The story is one of a woman using her sexuality to entrance and trap a man, followed by the brooding bitterness of his revenge. My suggestion in the novel is that the interesting story after the rivalry, is Mary's choice to be an ordinary Tudor wife and mother. The film, however, focuses on the drama rather than the humdrum and ordinary.

When I saw the film in its final cut I saw what I think will be a new telling of the story of Anne Boleyn, a story of ambition that turns to self-destruction, and of desire that turns to hate. It is not a film of the adventure of a woman who has the courage and determination to go against her society and seek and find an ordinary life. That is a story which perhaps could be told only in a novel. The film is on the big screen, the novel is on the small page.

They tell the same events but with a different emphasis. The title of the novel, and now the film, was always intended as a question that the reader, and now the viewer, can answer. Who is the most extraordinary heroine of this story, the famous Boleyn; and who is the other Boleyn girl?

The Other Boleyn Girl by Philippa Gregory
HarperCollins, £7.99

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