If the latest survey is to be believed, the only churchgoers in 30 years' time will be Sir Cliff Richard and Tony Blair. The Religious Trends report suggests that there will be fewer people attending churches than mosques by 2040, and that the Church of England will be in the red.

Is Britain a post-Christian society? And can it still be a Christian country if it becomes, as Cardinal Cormac Murphy-O'Connor put it last week, a God-free zone? I am not best placed to comment on faith matters, being a sort of moonlighting agnostic. But I am suspicious of any study that extrapolates the future by extending a straight line forward from the past. The report, published by Christian Research, assumes that half of all Muslims are active worshippers in mosques, and that they will continue to be. It is similarly simplistic about Christian worship and the figures have sparked an unholy row.

I am also suspicious of those who claim that Britain will cease to be a Christian country if average Sunday attendance passes some arbitrary threshold (at the moment 6.3 per cent of the population attend church on an average Sunday). Clerics like to believe that attendance is the same as faith, but I am not at all sure that it is. Secularists conclude that lack of faith makes Christianity a minority religion, and that we should rush to disestablish the Church of England. I am not so sure of that either.

The divine decline is indisputable. But it is not a recent phenomenon. In the early 18th century, the outlook for Christian worship was thought bleak despite the absence of Match of the Day and Nintendo Wii. There followed an unexpected boost from Methodist dissent, which lasted for about 100 years. Then from the late 19th century, churchgoing started on a decline that has been unbroken. Regular worshippers made up only 30 per cent of the population by 1900, down to 19 per cent in 1970 and 15 per cent in 1990.

Even at its peak, our Christianity seems to have had as much to do with pragmatism as faith. During the Victorian revival, it was useful to go to church, at least in the countryside, because the local squire was there. A few years ago Alasdair Crockett, of Nuffield College, Oxford, studying the religious census of 1851, found that the strongest correlation with churchgoing at that time was population density. Fewer than half of people in isolated rural areas went to church, until John Wesley's Methodist movement built chapels closer to them. In more densely populated communities, worship touched 90 per cent levels. But in the densest cities, where church spires were everywhere, attendance was lower.

Not being able to get to church easily was clearly a turn-off. But so, it seems, was not knowing or caring much for your neighbour. As communities weakened and the original fire-and-brimstone preachers faded, Methodism's decline was as dramatic as its rise. Even 100 years ago, rationality and the cities were the enemy of organised religion.

There is a fascinating debate to be had about cause and effect. But the only point I want to make is that being a Christian country has always been about more than belief in God and Sunday worship. In the 2001 census, seven in ten people described themselves as Christian, to the astonishment of many bishops; 22 per cent claimed to be still going to church at least once a year.

Britain is still a Christian landscape, dotted with spires. It is still a place of Christian ritual, where people go to churches to mark marriages and deaths. It still has some heroic pastors who help people cope through terrible times. These things are part of the fabric, but they are strangely absent from much of the debate about national identity.

I had not thought much about all of this until five years ago. My first child was a year old and my mother, who had always been a militant atheist, suggested I should start taking him to church. She thought he should “have the option” of being part of a religious tradition. I was stunned. My parents had reacted with detached amusement when I had flirted with churchgoing at the age of 13, a brief period that ended with my deciding that I could not be confirmed, because God would know that I didn't really believe the words I would have to speak. The vicar, I think, was floored by my pagan levels of superstition. My father, whose own father was a vicar, still sees religion primarily as device by which elites exercise power over the people. And I am inclined to agree.

Nevertheless, my mother had hit on something. I dutifully explored various churches. The first surprise was how much my son enjoyed the ritual, the kindness. The next surprise was how deeply the rhythm and the language resonated with me. The writers and composers of the best religious works can still sharpen the senses and infuse the spirit like nothing else. The hymns that we sang at school, the cadences of Bible stories, are part of my identity. What other identity can I have?

I have not sent my boy to a church school, but to a school that has hymns in assembly, as well as plenty of acknowledgement of other religions. If I don't expose him to that canon, what other can he have? I suspect there are many people who would regret the passing of the Church even if they never set foot in one. The Church of England is rather like the BBC, a beloved institution, mainly mush but with flashes of inspiration. Despite my criticisms of the trend projections, it may be that one day we will have to contemplate paying a church licence fee.

Like TV I may not use it often, but I'd pay for the option. Because it represents something precious, something that we take for granted, and which is presented as faith but is also about the national soul.

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