Forte and Pullman had a "dream casting session" a decade ago, when she negotiated an option to Pullman's work, to which Pullman added: "I always wanted Nicole Kidman for her extraordinary quality of being warm and cold, terrifying and seductive." He also envisaged Laurence Olivier, circa 1945, as Lord Asriel, a role eventually taken by Craig because Olivier "wasn't available".

*****

Although Lewis's and Pullman's religious beliefs are radically different, Lewis's Chronicles of Narnia shares much with The Golden Compass: talking animals, witches and child protagonists travelling to fantasy worlds. But Pullman's coup is all his own: the daemon, pronounced "demon". In The Golden Compass, almost everyone has a daemon, an animal that is another version of the person to whom they belong. They feel the same things, mentally and physically. The daemon is an idea borrowed from Socrates, who believed he had a divine presence within himself. He called it a "daimon" and it would warn him if he was about to do something bad.

*****

For Pullman, the daemon was also a great literary device. As he told the Oxford audience: "The moment I thought of daemons was on the 16th draft of the first chapter. Before that I had to tell the reader what Lyra was thinking. I realised then I didn't have to explain so much. You don't need exposition. Exposition kills the flow of the narrative.

"The best advice ever given to a writer was by Raymond Chandler, who said, 'When in doubt, have a man come through the door with a gun.' This works. If you're stuck with the story, it moves it on like nothing else." Lyra's daemon, Pantalaimon, "was my man coming through the door with a gun. It was a wonderful moment when I realised that."

Author Philip Pullman has attacked plans to turn The Chronicles of Narnia into a movie series, calling CS Lewis' books "racist" and "misogynistic". The first film in the series - The Lion, The Witch and The Wardrobe - is due to be released in December. His Dark Materials author Pullman said the 1950s stories were "reactionary". "If the Disney corporation wants to market this film as a great Christian story, they'll just have to tell lies about it," he told The Observer.

"It's not the presence of Christian doctrine I object to so much as the absence of Christian virtue. The highest virtue, we have on the authority of the New Testament itself, is love, and yet you find not a trace of that in the books."

The Narnia books, Pullman said, contained "...a peevish blend of racist, misogynistic and reactionary prejudice; but of love, of Christian charity, [there is] not a trace."