The latest data release from the ONS's integrated household survey shows a continued, slow decline in Christian affiliation, a small but significant increase in the number of people who profess no religion, the sustained growth of Islam and stability or decline in other religious groups.

The headline figures suggest that the United Kingdom remains a predominantly religious and mostly Christian country. Almost seven in ten (68.5 per cent) identify themselves to researchers as Christians -- far more than the 15 per cent who regularly attend church. Less than a quarter (23 per cent) profess no religion at all (although in Wales, the figure is considerable higher, at close to one in three. Of the population as a whole, 4.4% is Muslim -- more than all other minority faiths put together -- but still less than one person in 20. (The full IHS figures can be found here.)

This picture of stability may be something an illusion, however. The last time this survey was conducted, in 2009-2010, the figure for Christian affiliation was 71.4 per cent and for no religion was just 20 per cent. A movement of 3 per cent from a Christian identity to a non-religious one in a single year is potentially a dramatic one. The annual population survey, which has included a religion question since 2004, records what looks like a consistent pattern. In 2004-2005, the figures stood at around 78 per cent Christians and less than 16 per cent having no belief. Then, 3.2 per cent were Muslim. In every subsequent year, the number of self-styled Christians has declined -- and most of that decline can be accounted for by an increase in non-belief. (For a detailed breakdown of the statistics, see this EHRC survey here.

Now, look at the age profile of belief in Britain. According to the latest IHS, Christian affiliation is strongly correlated with age. No fewer than 87.6 per cent of those over 65 define themselves as Christians and almost 80 per cent of those aged over 50 but below retirement age. The 25-34 age group would seem to be the least religious, with just over half calling themselves Christians and about a third having no affiliation. At the same time, growth in Islam is taking place predominantly among the young. Almost 8 per cent of under 16s are now counted as Muslim, compared with a mere 1 per cent of those over 65.

There are various possible explanations for the age differential. One is that people are drifting away from religion in early adulthood but returning to it in old age when, among other things, they are more preoccupied with thoughts of death and a possible afterlife. There may be some truth in this. The new figures suggest that there is more religious attachment among those under 24 (and especially under 16) than among their slightly older peers. But not much. Another possibility is that younger people are simply more honest -- that older respondents grew up at a time when to admit to having no religion was less socially acceptable than it is today and have retained a habit of pretending to believe.

The most likely scenario, however, has to be that Christianity is contracting in the UK at a steady and observable rate, a long-term trend that has not been altered significantly by the increasing profile of religion in the media, politics and public debate over the past ten years.

It's not all bad news for Christian leaders. The UK remains theoretically a Christian majority country and is likely to be so for many years to come. The secularisation of society does not seem yet to have reached a tipping point at which attachment to Christianity -- however notional -- collapses. Lack of affiliation with any religion, moreover, is not the same thing as out-and-out atheism -- it can encompass a wide range of vaguely religious and spiritual beliefs. Membership of many evangelical churches continues to grow. And the churches retain formidable resources in terms of organisation, political influence and social prestige.

The days of most people automatically ticking the box marked "C of E" may well be numbered. And if the Christian majority continues to shrink, the historic privileges of the established church -- and of Christianity generally -- will become ever harder to defend.