The winners of the Carnegie and Kate Greenaway Medals, the Bookers of children’s literature, are announced this week.

Carnegie Medal winner Philip Pullman believes that something precious is lost between the ages of nine and 13. In Northern Lights, his most challenging work so far, he is helping the most jaded adult regain a sense of “the grace, the innocence, the singleness that children lose”.

The novel is the first volume of His Dark Materials, a trilogy inspired by Milton’s Paradise Lost with the myth of the Temptation and Fall at its heart. This, Pullman believes, is “the central Western human myth, not only in the Christian senseIit’s what happens to us all when we gain self-consciousness.

“Children at the stage in their lives before this happens are wonderful to write for. You can encompass large themes. They don’t yet think they have other things to think about like the pressures of everyday life, emotional problems and financial problems. As adults we lose sight of the big questions, although we can come back to them.”

In Northern Lights, that pre-pubescent energy is a commodity as sought-after as cocaine or diamonds, and the forces of cruelty and corruption are unleashed in its pursuit. Pullman’s heroine Lyra, the most intriguing 11-year-old in contemporary fiction, fights back with few resources except a strange contraption - a meter for reading the truth.

Pullman sends her on a quest to an Arctic wasteland inspired by Mary Shelley’s Frankenstein, scattered with armoured bears and flying witches, with mystical universes glimpsed beyond the Aurora. As well as her daemon - all the characters in Northern Lights are accompanied by their souls in animal form, like witches’ familiars - Pullman has given her a charmed childhood to stave off the inevitable Fall. She has been brought up absent-mindedly by a gaggle of Oxford dons (Pullman has taken liberties with the institutions and architecture of his home town to expose a collegiate underbelly) and runs semi-wild in the clay beds and back alleys, never patronised or deceived and taught as much as she wants to learn.

“They provide for her in a casual way and leave her alone,” says Pullman. “What more could a child want?” He is glad that his teaching experience - 12 years in Oxford middle schools - is all pre-national curriculum. He has also just stopped teaching part-time on PGCE and BEd courses at Westminster College, Oxford.

His passage into full-time writing has been eased by the critical and commercial success of Northern Lights, on top of a healthy track record in fiction (his historical mysteries such as Ruby in the Smoke have been especially well received). “Success is hard to quantify. I used to think of publishing as throwing a stone into a swamp. You think nobody’s taking any notice, the frogs are still croaking. You don’t often meet other writers and you don’t know if anyone’s reading you. Now it seems the bubbles on the surface of the swamp are bigger than I thought.”

The Carnegie Medal, awarded by librarians, has the status of the Booker Prize in the children’s literature world without the hype or the big money - Pullman and the Kate Greenaway Medal winner, P J Lynch, will each receive Pounds 1,000 worth of books from the sponsors, Peters Library Service, to give to the children’s library of their choice.

Northern Lights, published by scholastic, is physically and intellectually the weightiest volume on this year’s shortlist. Accessible to readers from eight-year-olds to adults, it is a deceptively learned book with a background of custom-built technology which does not emerge until a second reading.

Pullman has created his own laws of physics and his own belief system. He describes himself as “a Church of England atheist - a 1662 Prayer Book atheist in fact” and Lyra’s universe is a moral one, although the Church rulers are corrupt. His grandfather was a Norfolk clergyman and, he says, “I was taught right and wrong by example rather than by threat.”

A tantalising epigraph promises a second Dark Materials volume “set in the universe we know” which is at the “carpentry” stage, Pullman says, and due out next year. We haven’t seen the last of the evil Mrs Coulter, or of Serafina Pekkala’s witches, or of the jovial Texan pilot Lee Scoresby. The final part of the trilogy is still in Pullman’s head - a strange and wonderful new treatment of an old story.