CS Lewis, the author of the Narnia stories, with which Disney hopes to establish a blockbuster movie franchise to rival Harry Potter, was "absolutely opposed" to the idea of a live action version of the stories, it has emerged.

The author made clear his distaste for the idea in a hitherto unpublished letter to a BBC producer with whom he collaborated on a radio version of The Magician's Nephew, chronologically the first in the much-loved series of fantasy tales which double as Christian allegory.

In the letter, dated December 18 1959, Lewis made clear he approved of the radio version of the book produced by Lance Sieveking, a pioneering BBC radio and television producer. But in letters written shortly before the death of his wife, Joy, Lewis also said he was "absolutely opposed - adamant isn't in it! - to a TV version" of any of the books. "Anthropomorphic animals, when taken out of narrative into actual visibility, always turn into buffoonery or nightmare. At least, with photography," he wrote.

A cartoon version would be "another matter", he said. But Lewis, who died in 1963, added: "If only Disney did not combine so much vulgarity with his genius." In conclusion, he said that "a human, pantomime Aslan would to me be blasphemy".

Whether he would have thought differently had he foreseen the lavish special effects on which Disney would spend a large portion of the reported £85m the film took to make will be contested by fans on internet message boards devoted to the author and his work.

The new Disney version, The Chronicles of Narnia: The Lion, the Witch and the Wardrobe, uses a computer-generated version of the noble lion Aslan, voiced by Liam Neeson. It also uses 1,700 special-effects shots and computer-generated sequences.

The marketing machine behind the film, which opens on December 8, has already swung into action. Disney has signed a string of tie-in deals with companies from Kodak to McDonald's, and more than 60 licences have been granted to manufacture everything from board games to replica swords.

Lewis's estate, partly overseen by his stepson Douglas Gresham, who co-produced the film, has to date been sparing in allowing broadcasters and film studios to develop projects based on the books.

In 1988 the BBC was allowed to produce a well-received version of The Lion, the Witch and the Wardrobe. Film versions were mooted but never reached the screen until now.

Mr Gresham finally entrusted the rights to Walden Media, the production outfit owned by the billionaire Christian financier and film producer Philip Anschutz, who enlisted Disney to finance the project. The film is expected to be a hit on both sides of the Atlantic after winning the support of evangelical organisations drawn to its Christian message.

The letter has remained in the possession of Mr Sieveking's son Paul, a founding editor of Fortean Times magazine, since his death in 1972. It finally came to light when his wife, Val Stevenson, posted it on Nthposition.com, the literary website of which she is editor.