PHILIP Pullman has agreed to meet on the condition that I don’t ask him questions he’s been asked a million times before. That’s fine by me; Oxford is seven hours from Glasgow by train, a long way to go to replicate someone else’s interview, but it’s a revealing caveat all the same. Pullman, who has been described as nothing less than the greatest storyteller of all time, is unwilling to tolerate a failure of imagination from anyone else.

We’re in his publisher’s office, less than a minute as the witch flies (although probably a quarter of an hour in Hobbit strides) from The Eagle and Child, the pub where JRR Tolkien and CS Lewis compared lords and lions so long ago. Pullman actually met Tolkien while studying English at Oxford in the sixties, and has recently been in the papers for describing Lewis’s Chronicles of Narnia as “blatantly racist” and “monumentally disparaging of women”.

In fact, he has now usurped both authors as king of the Inklings, a massively successful writer of children’s books who sprinkles a breadcrumb trail of subversion through the enchanted forest of his fabulous stories. While Lewis composed hymns to Christianity, Pullman’s His Dark Materials trilogy is an operatic malediction, a demolition of organised religion, God’s house, and all his mansions. And it helps his cause – and bank balance – no end that the novels are also rip-roaringly unputdownable. He has sold around one and a half million of them, and in January became the first children’s writer to win the Whitbread book of the year prize (attendant booty: £25,000).

Today, Pullman is happy to sit down and take stock of how his life has changed. “You know you’re famous,” he smiles, “when your trousers split and they put it in the paper.” The weekend before our interview, he was at the Hay-on-Wye literary festival, “and purely by chance, as I bent over to go under a fence, my trousers split from stem to stern. Now, that would not have been reported before, but there it was in the Independent.”

And how is he going to top that when he appears at the Edinburgh Book Festival in August? “Perhaps I can arrange for them to fall down completely.”

As Pullman’s profile has risen, a certain mythology has grown up around him, a set of facts which, by law, must be repeated in every article. Here is what we know.

He writes in a shed at the bottom of his garden. The shed is home to a six foot long rat, a prop salvaged from a play he produced. Every day he writes 1000 words by hand, using a ballpoint pen on narrow, lined A4 paper with two holes, not four. In this way, he continues from morning until 1.45pm, then stops for lunch and Neighbours.

This routine is important. Pullman thinks of himself as a craftsman, an artisan rather than an artist. He believes in neither inspiration nor writers’ block, although he does believe that both are the refuge of “fucking amateurs”. He, on the other hand, is a professional, a man who has learned his trade over the course of 30 years and more than 20 books. The His Dark Materials novels – Northern Lights (1995), The Subtle Knife (1997), and The Amber Spyglass (2000) – are the spoiled triplets of the Pullman brood, lavished with public love and attention at the expense of their older kin.

“The trilogy came at the right time in my life,” he says. ‘”I was 46 when I started writing this, and I knew how to tell a story by then. I’d served my apprenticeship. If I’d had this idea 30 years ago, I don’t think I would have dealt with it very well.”

The books are rich and sophisticated; to summarise is to reduce them, but here goes. They concern the adventures of Lyra and Will, two 11-year-olds, both from Oxford, but from parallel universes, who discover that – despite being rather ordinary children – it is their destiny to kill God, re-enact the Fall of Man, and establish “the Republic of Heaven”, a secular paradise, on earth.

Along the way there are armoured bears, sexy witches, satanic scientists, tiny spies on dragonflies, a female villain who makes Cruella De Vil look like Kylie, and gay angels with a taste for Kendal Mint Cake. There are also daemons, Pullman’s greatest creation, shape-shifting creatures in animal form, constant companions to the humans of Lyra’s world, in fact part of their very essence. But what exactly are daemons? The human soul? Our sexuality? Pullman is never entirely specific, although he thinks that if he had a daemon, it would probably be a raven, “because that’s the bird in North American mythology that stands for the trickster, the storyteller, the creator”.

Of course, this fabulously rendered bestiary (did I mention the foxes that can speak only in the present tense?) is as nothing compared to the splash caused by the anti-church polemic at the heart of the books. Writing in The Mail on Sunday, Peter Hitchens said that Pullman was the most dangerous author in Britain, while the Catholic Herald declared the books were “worthy of the bonfire”. If the Archbishop of Canterbury were in the business of dishing out fatwas, Pullman would most probably have been stoned to death outside St Paul’s by now. Certainly The Amber Spyglass is much more ferocious an attack on religious dogma than, say, The Satanic Verses.

In the flesh, Pullman does not smell even faintly of brimstone. At least Salman Rushdie had the good grace to look like Lucifer, this guy isn’t even trying. He looks, in fact, exactly like Heinz Wolff from The Great Egg Race; a professorial 55-year-old in short-sleeved pink shirt and blue jeans, given to saying things like “Eternal life is the most cruel of tortures, even for God”, and “There’s a lot of gnosticism about at the moment; look at The X Files. Pure Gnosticism!” You are always aware, interviewing him, that you are dealing with a vast intellect. I keep expecting the dome of his head to flip open on a hinge and his cerebral cortex to take a bow.

We talk for a while about his grandfather, an Anglican priest who lived in a huge, draughty eighteenth-century rectory. “I spent a lot of my childhood there,” he says. “After my father died, my mother lived in London on her own, working for the BBC, and my brother and I lived with our grandparents in Norfolk. Grandpa was the centre of our lives, really.” The old man was a great storyteller. His sermons could be quite formal, but off-duty he was full of tales of cowboys and Indians. From his grandfather Pullman inherited an encyclopaedic knowledge of the Bible and a taste for tall tales; he got to know his enemy and developed the skills with which he would later attack it.

What would his grandfather have thought of His Dark Materials? “Well, I think he would have been saddened by the fact I was attacking the church. He’d think I was wrong. But he was a sensible enough man to look behind that at the morality of the story.”

In the trilogy a premium is placed on love and compassion. “Those values are very important. They are the foundation of the Republic of Heaven. I always think it’s a colossal nerve of Christians and Muslims and Buddhists and Jews and other people to say that all human morality comes from religious teaching. It doesn’t at all. Purely coincidental. We’d be just as good without them.”

His father, an RAF fighter pilot, was shot down and killed in 1953 while flying a mission against the Mau Mau in Kenya. Pullman has his doubts about what exactly happened; he hints at some sort of cover-up, and his fiction is informed by this mystery. “A lot of my stories have dealt with characters who have lost a parent, about whom there is some mystery involved,” he says. “I don’t know the real circumstances of my father’s death, and I probably never will. So I continue to puzzle about it, and inevitably that enters my mind at some subconscious level, and I keep coming up with stories about characters who are in this predicament. It’s not uncommon for writers of children’s fiction to have lost a parent. Maybe we tell ourselves stories as a way of explaining the absence.”

In The Amber Spyglass, Lyra and Will visit the land of the dead, where Will is reunited with his father. I tell Pullman that, weirdly, when I read this section of the novel, I actually felt physically heavier. “Good,” he smiles. “I’m glad you felt like that, because so did I when I was writing it. I had to push myself to imagine those things. When I realised Lyra and Will would have to go to the land of the dead, I felt a burden settling on my shoulders. I dreaded it.”

The land of the dead – a barren, blanched limbo inhabited by spiritless ghosts with “voices no louder than dry leaves falling” – could only have been dredged up from the imagination of someone with the most profound experience of despair. In his mid-twenties Pullman suffered from a bout of depression. He felt suicidal. Talking about this somewhat unwillingly, he seeks sanctuary in semantics. “I prefer to call it melancholy, which is the old word, of course. It’s a melancholia, even. Even melancholy isn’t quite right, because that sounds like a kind of great sadness, but it’s far fiercer than that. It’s deadly.”

What brought it on? “I don’t know. It just kind of crept up on me when I wasn’t looking.” Was it to do with his loss of faith? “It might have been. But by the time I had my little episode, I was 26. And it had been a long time since I had ceased to believe in God, so I don’t think there is a direct connection. But you can be overtaken by this if you’re not careful. And I’ve been careful since.

“Doctor Johnson, a great hero of mine and a profound melancholic, said very wisely that if you are solitary, be not idle; ‘if you are idle, be not solitary’. The worst thing is having nothing to do and being on your own. You might as well kill yourself straight away and be done with it. So I try to keep busy.”

How, I ask, did you come to feel better? “I suppose the help of my wife. The baby. We had a young child. The sense that these people were precious and important, and if I, uh, wanted to see my little boy grow up, as I did, I’d better stay around. And, I suppose, medical science. I went to the doctor and I got some anti-depressants. They calmed me down a bit. And just a sense of work. A job to do. I’ve got a job here, I’ve got something to do. There’s a reason for being here: I’ve got to write books.”

Make no mistake, Pullman is a man with a mission. He believes this is his destiny. All the meaning that he does not find in Christianity he gets from storytelling, and the unique ability of humans to transport each other with words. “After nourishment, shelter, and companionship,” he says, “stories are the thing we need most in the world.”

Of course, when your stories are as popular as Pullman’s, you can find you also need a good accountant. The film rights to His Dark Materials have been sold to New Line, the company that made Lord of The Rings, and it seems likely Tom Stoppard will write the script, while Nicole Kidman has been mentioned as a possible star (“I’ve expressed all kinds of interest in Nicole Kidman,” says Pullman with a jolly leer). He is currently writing a short “fairy story”, and after that will turn his attention to a fourth His Dark Materials novel which will not, despite rumours, be a prequel. It will “look at other aspects of that world”, but beyond that Pullman isn’t saying much. “I shall have to swing on my chair for six months before I know what I’m going to do with it.”

Two things are certain: the book will be eagerly anticipated and will be worth the wait. Pullman has mastered his art and is at the top of his game now. He has had difficult periods in his life, but surely a man who believes so firmly in the power of a good story well told deserves his own happily-ever-after.