We agreed to disagree, God and I, more than 30 years ago. I concluded that He was a metaphor, He begged to differ, and things went downhill after that. Yet for all I've led a secular life in a country regularly described as the least religious in the world, God takes some shaking off. His teams say He is omnipresent and though I don't agree, He has quite a property portfolio, many voluble cheerleaders and, if official statistics mean anything, the tacit support of most of the country. Then there are churches! The minarets! That slot on the Today programme . . . If God is a metaphor, He's a pretty noisy one.

The last census showed that more than 72 per cent of British people called themselves Christian, around 3 per cent Muslim (it will be more by now) and half a per cent Jewish; so that's more than three-quarters for the Sky-God, as Gore Vidal puts it, or the Abrahamics. Just under 15 per cent said they had no religion, and just under 8 per cent ignored the question, being either so secular that they didn't get it, or perhaps people who think God disapproves of questionnaires.

Now, of course plenty of the three-quarters only mean they quite like humming the songs, or feel sentimental when they roll up to see Fiddler on the Roof. They are religious in the way that someone who has bought a pair of trainers is an athlete. They might be mildly offended by the New Atheism, the broadsides of Richard Dawkins, A C Grayling or Christopher Hitchens, but not enough to turn up and listen to a vicar putting the other side. The 2005 Church Survey, assessing the size of congregations in the country's 37,000 churches, reckoned that only 6.3 per cent of people showed up regularly. A thousand people joined a church each week, but 2,500 left one.

Behind the raw figures, there is plenty of change. Driving back from work on a Sunday, I pass big groups of black kids outside church, clutching their Bibles. The decline in attendance has slowed only because of immigrants: more Poles boost Catholic churches, and yes, in inner London, for instance, less than half the churchgoers are white. Above all, there is the rise in British Islam, both in visibility and numbers.

Much of this is a familiar story for the modern British. The Church of England suffered one of its most precipitous periods of decline from 1935-45 and overall church attendance after the Second World War was boosted by immigrant Irish and refugee Poles. The rise in the Catholic Church has been a long, slow curve, not a recent burst.

Crazy about moderation

What has really changed is God in the public culture. He may still be in the Garden, in private places, but think of Britain in the 1940s and 1950s. Think of the influence of religious poets (T S Eliot, the later Auden), of religious art and architecture (the rebuilding of Coventry Cathedral), of religious music (Britten's hymns, Missa Brevis and carols) and of religious writers such as C S Lewis, and it's clear that Christianity at least has moved from a powerful cultural position to a marginal one. Add to that the saturating influence of hymn and psalm settings and the near-ubiquity of church weddings and funerals, and you see a really big change. Go a little further back and think of Victorian Britain: a much smaller population and churches which now seem ludicrously large and empty.

I think it is simply because the once-dominant church, the Anglican one, and for that matter the Church of Scotland, in which I grew up, were simply never as aggressive and authoritarian as the Catholic Church, or any variety of Islam. This is a watery, temperate country with a long and soundly based suspicion of intensity. Apart from Northern Ireland, the last time the British were really intense about religion was in the 17th century. If you want to imagine what the civil wars were like for many villages and towns, with neighbours killing neighbours and families dividing, think of the Sunni-Shia war in Iraq, or the worst of times in the post-Yugoslavia Balkans. Oh, and we had our Taliban, too, from John Knox's version in Scotland to the statue-smashers and dance police of Cromwellian England. The misogyny that allows Muslim women to be stoned or beaten for alleged sexual transgressions is vile, as vile as our one-time relish for roasting witches. Though no one knows the real figures, it is thought that some 40,000 women were killed here in the "burning times".

Somehow, the folk memories remain for longer than his torians acknowledge. It's less that the British are irreligious, or even secular, though many of us are. It's not that the Brit-ish are hostile to God. It's that they are hostile to fervour, to fanaticism, to taking anything, even the Meaning of Life, too seriously. It's a lesson learned long ago, the hard way, and never quite forgotten. And it gets more important, not less. A small, crowded place, the world's island, can't afford assertive, flaming certainties. Something, or somebody, might catch fire.

It's important to try to rein in Muslim extremists. It matters that more level-headed imams gain ground. For a country in a world that will depend on science to get us through hard times ahead, it is vital not to equate creationism with Darwinism, or to allow any religious group to dictate to others how they live their lives. But as people come here, and live here, and look around and wonder about God and the British, the real prize is to persuade them just to calm down. He may be among us. Or, as I think, He may not. (I take no pleasure in that, by the way: praise, in the sense of drinking in the delight of life, is good, and asking, "What's it all for?" is inevitable. Wondering about death is, too, and communal singing is a wonderful thing. It's just the facts I have trouble with.)

But either way, if God is still with the British, He will be quiet, understated, embarrassed by enthusiasm, and no supporter of violence, or even violent words. Some think God is a bright-eyed woman; others think He is a local and shy affair, fluvial, bosky and - in Louis MacNeice's phrase - incorrigibly plural. Over time, I think, His property portfolio will shrink and He will quit any involvement with the state, and a good thing, too. But the problem isn't God. The problem is anger.

Andrew Marr hosts a Sunday morning TV show on BBC1 and Radio 4's Start the Week. His next book will be a history of modern Britons from 1900-45

A brief history of God

1200BC Zoroastrians in ancient Persia begin to speak of a single, unchanging God

1200-400BC Judaism develops as a faith in one God for a single, chosen people

4thc BC Plato describes "the divine creator" as the highest and most perfect being

1stc AD In Palestine, Jesus preaches that there is one God - the Father - and he is His son

325AD The Nicene Creed defines Christian belief in the Trinity

613AD In Arabia, Muhammad preaches that Allah is the one eternal, transcendent God

1517AD Martin Luther's teachings begin the Protestant Reformation

1882AD Friedrich Nietzsche announces that "God is dead"

1900sAD Sigmund Freud describes God as a projection of the mind

Research by Aditi Charanji