OXFORD author Philip Pullman has written a new book, aimed at fans of his award-winning His Dark Materials trilogy.

Earlier this month, Mr Pullman, 61, attended the premiere of The Golden Compass, alongside film stars Daniel Craig and Nicole Kidman.

He said he was delighted with the £90m movie adaptation of Northern Lights, the first book in the trilogy, and hoped films would now be made of the second and third instalments, The Subtle Knife and The Amber Spyglass.

Mr Pullman said he also wanted to concentrate on writing his next full-length novel, The Book of Dust, which could be published in 2009.

But fans will not have to wait until then for his next book. This spring, he will release Once Upon A Time in the North - a companion to the trilogy.

Mr Pullman said: "It's a separate story that takes place some time before Lyra was born involving the two characters Lee Scoresby, the balloonist, and Iorek Byrnison, the armoured bear.

"You will be able to read about their history and how they first met. You see when we meet them in Northern Lights they have known each other for years and fought in various campaigns together.

"It's a bit longer than Lyra's Oxford, the other companion book for the Dark Materials trilogy, which is about 8,000 words. This story is about 20,000 words.

"I hope people who have read the other books enjoy it."

Nina Douglas, a spokesman for Random House, which incorporates the David Fickling imprint, said: "We are very excited that Philip Pullman has written a second companion piece to His Dark Materials.

"Like Lyra's Oxford, it will be illustrated by John Lawrence, and this time it will contain a fold-out game.

"We are planning to publish the book in April, about the same time that the DVD of the film is scheduled for release, and around the same time as the Oxford Literary Festival."

It is understood Mr Pullman wanted to write a story about Iorek Byrnison and Lee Scoresby meeting when they were young.

A story about Will from the trilogy could follow later in a small green book.

Several scenes from The Golden Compass were filmed in and around Oxford and it is estimated that the city's connection with the film could provide tourism businesses with a £15m boost.

Last week, Mr Pullman spoke out against plans for a four-storey block of flats in Jericho, which provided the setting for scenes on the canal in Northern Lights.

Councillors rejected the proposals by Spring Residential but the company is planning to appeal against the decision.