A request from the Archbishop of Canterbury, Rowan Williams, to explain what I mean by calling myself a "Church of England atheist" is not to be ignored. I'd better begin with the word "atheist".

That's the word I prefer to use, because I'm almost certain that there is no God, no Creator, no heaven, no hell. I have seen no evidence for them. I have never had any experience of being spoken to by God or of seeing him in the sky or in a tree or anywhere else. Wherever I look, whether in the present day or in recorded history, I see the processes of nature and the activities of human beings but no sign of God. That's why I call myself an atheist.

However, just because I haven't seen or heard him, it doesn't mean that God doesn't exist. He might have made this suburb of the universe but then withdrawn to another. He might have grown old and died. He might have been overthrown and exiled.

I don't know and those things are possible, remotely; so, to describe myself with strict accuracy, I should say that I'm an agnostic - or, to use a term invented by the neuroscientist David Eagleman in his ingenious little book Sum, a "possibilian".

As far as I can tell, God is not here now and he never was. As for the Christian claim that Jesus was his son, who existed before the world was created and who was given to the world so that his death might save us all from sin, it strikes me as unlikely, to say the least.

On that claim is founded an enormous edifice of theology, which, for all its absurdity, is clearly not the work of stupid people. The enormous structures of elaboration, qualification and speculation are a striking testament to human ingenuity and inventiveness. But I think that it's a collective work of fiction.

Nevertheless, I do find religion very interesting. To my mind, William James, in The Varieties of Religious Experience, takes the right stance towards it. He ignores the theology and looks calmly at the psychological effects and consequences of belief, making human sympathy the key to his basic approach:

Religious melancholy, whatever peculiarities it may have qua religious, is, at any rate, melancholy. Religious happiness is happiness. Religious trance is trance . . . Who does not see that we are likely to ascertain the distinctive significance of religious melancholy and happiness, or of religious trances, far better by comparing them as conscientiously as we can with other varieties of melancholy, happiness and trance, than by refusing to consider their place in any more general series and treating them as if they were outside of nature's order altogether?

Religion is something that human beings do and human activity is fascinating. I have never had an experience that I could call religious, though I have known two or three short passages of intense, transcendental feeling - that is to say, experiences of about 15 to 20 minutes, during which my perception of things in the external world (one was a storm on a beach; another was a journey home on a winter evening on the Tube and bus from Charing Cross Road to Barnes) seemed to become enlarged and clarified to include many things, all of which I was able to see without losing sight of everything else.

These visions of the real world were laced through with patterns and connections and correspondences. They were accompanied by a feeling of intense, calm excitement. I felt that I was seeing the truth, that all things were like this and that the universe was alive and conscious and full of urgent purpose.

Perhaps "transcendental" is the wrong word: there was nothing other-worldly about these moments, nothing "spiritual". Rather, this material world was more intensely present and alive than I had ever felt it to be before.

I don't know what happened to evoke such a feeling. Certainly, drugs had nothing to do with it. But I think that if my mind had been inclined to religious explanations, it would have been easy to feel that I had been granted some kind of vision.

These were my only experiences of anything that could be called "visionary". But why "Church of England"? It isn't a term that might as well be arbitrary or made on aesthetic or whimsical grounds. Martin Rees, until recently president of the Royal Society, has spoken of his desire to be buried in an English country churchyard, according to the rites of the Anglican Church. Despite his lack of belief in God, he feels an attachment to what he calls the "customs of [his] tribe".

I completely understand. If I'd thought of that phrase before he did, I would have used it myself. I am English and I was brought up to go to church every Sunday, to say my prayers, to behave in certain ways in church - to bare my head, for example. I was baptised when I was a baby and confirmed when I was 12.

I belong to the last generation that was brought up using the language of the 17th century as the appropriate, or the natural, or at least the respectful way to talk to or about God. Many have lamented the way in which the King James Bible and The Book of Common Prayer have been replaced by translations and forms of service that lack the majesty, the beauty, the poetic resonance, and so on, of the older versions. All of that is worth saying and I agree with it up to a point, but we can make a fetish of these things. The Bible I turn to first these days if I want to be sure of the meaning of a passage is the New Revised Standard Version.

Nevertheless, those resonances remain. Some of them are personal. I wouldn't expect any­-one else to love the collect from the evening prayer - "Lighten our darkness, we beseech thee, O Lord; and by thy great mercy defend us from all perils and dangers of this night; for the love of thy only Son, our Saviour, Jesus Christ. Amen" - for the reason I do, which is that my grandfather taught it to me when I was six or seven so that it would make me feel safe in the dark, and it did.

He was a clergyman and it's his voice I hear when I remember the beautiful prayers from matins or evensong or the Communion service. We can't abandon these early memories, by which I mean both that it's impossible and that it would be wrong. It is those that have made us and not we ourselves. Even if I became a Buddhist, I couldn't help but be a Church of England Buddhist.

Consequently, when I survey the wondrous mess that the sexophobic zealots in the Anglican Church have tried to bring about in recent years, I feel both distress and anger. None of my business in a way, because I'm not a believer, but at the same time it is my business: because of those memories of mine and because the Church of England is the established church of this nation. It belongs to all of us. We're all entitled to hold opinions about it.

And these demented barbarians, driven by their single idea that God is as obsessed by sex as they are themselves, are doing their best to destroy what used to be one of the great characteristics of the Church of England, namely a sort of humane liberal tolerance, the quality embodied in the term "broad church". A broad church is exactly the sort of church I like. Inclusive, not exclusive; more concerned with helping people in distress than in maintaining strict forms of worship and a literal reading of the Bible; and, above all, characterised by a dislike of fanatical inquisition into beliefs and motives. What goes on in people's minds and hearts is their own business and, what's more, it's likely to be largely unknown even to them. What matters is not what they believe, but what they do.

The Church of England, at its best, knew that and acted on it and, while any scraps of that tradition remain, I'm happy to be known as a Church of England atheist.

Philip Pullman's latest book is "The Good Man Jesus and the Scoundrel Christ" (Canongate, £10.99). The "His Dark Materials" trilogy - "Northern Lights", "The Subtle Knife" and “The Amber Spyglass" - is published by Scholastic (£7.99 each)