Every second Friday, before the evening Shabbat service, Reform rabbi Jonathan Romain holds an instruction class for converts. Most attend because they are marrying Jewish partners, but some come for a different reason. Disillusioned with other faiths, they hope Judaism is the answer to their religious quest. Numbers of such people are tiny: a handful in Romain's class of 20 in his synagogue at Maidenhead, Berkshire, and just 27 in the entire liberal reform movement last year. But they show that even Judaism - which does not actively seek new adherents - is affected by a rising tide of conversions, among both major faiths and minor cults, in spite of dwindling attendance at many traditional places of worship.
It is estimated that 1,000 people a day find a new religion. This is a complex pattern with every imaginable permutation. Some with no faith are finding a god or guru for the first time; others are switching one set of beliefs for another. Methodists becoming Moslems and Catholics becoming Jews is unusual; Jews choosing Buddhism is bizarre, but it is happening. And on the fringe, the choice is bewildering: it is estimated that some 400 cults have emerged since 1945. Romain knows about all these crosscurrents; how for some, religion is added to the pick and mix menu of their lifestyle choices. For as well as observing, and encouraging, interested non-Jews to convert, he has researched the wider trends for a new book, Your God Shall Be My God.
Religion has become "much more a matter of choice than of inherited tradition", he says. More of the young are deciding for themselves, rather than following their parents' beliefs. At the same time, it is becoming privatised. "Religion was once a family affair - the family that prayed together stayed together, that sort of thing. Now it's very much a personal hobby. One partner will go to a service, the other to a car-boot sale, the children go fishing - and they all meet up for Sunday lunch with no traumas or raised eyebrows, even."
Changes in the education system and in society at large are speeding the multi-faith mix. Christianity is still generally given primacy in schools, but it is quite usual for pupils to be taken to a mosque or a Sikh temple; and to hear from a rabbi or a Buddhist.
Inter-religious marriages - and remarriages - are increasing: 65% of Catholics and 44% of Jews marry outside their faith. Some adults, and their offspring, are in effect serial converters. Romain knows a family where 11-year-old Darren is on his third religion: born a Methodist, his mum later married a Catholic but then divorced and married a Jewish man. Soon the boy will be preparing for his Bar Mitzvah.
This whirlpool of activity, though, sits in a sea of apathy: only 15% of the population attends some form of weekly worship. Yet despite this decline, hundreds of missionaries are busy, huckstering their religious wares.
Romain identifies four main groups of people interested in what's on offer: first-timers, with no previous religion; born-agains, whose latent attachment flares into fervour; denominational-switchers, who move, for instance, from one branch of Christianity to another; and total transferees, who abandon one creed for a wholly different one.
The way religious conversion occurs similarly falls into one of half a dozen categories: intellectual (where the decision is rationally arrived at through study); mystical (the result of an "out of the blue" religious experience); experimental (people looking for a faith that is "relevant" to their needs); affectional (joining the faith of a spouse); revivalist (outreach by a creed wanting new members), and coercive (cults pressurising individuals to join up).
Analysed in this way, it is tempting to see religion as a product, with different marketing techniques being used by the promoters of the various brands as they compete for customers. This would be cynical if it were not a fact that some strands of Christianity have for decades been taking a page out of the marketing gurus' manuals. And some faith-seekers have been "shopping around", as they would for any other item. Consumer testing is a simple way of putting it but, at a sophisticated level, that is what informed people are doing.
Lorna Jacobs, a member of Romain's synagogue, grew up in a home counties Anglican family; gave American revivalist Billy Graham a spin as a teenager; sat quietly with the Quakers for a few years, then gravitated to Judaism. "Christianity seemed to me like it was all hope and no results," she says.
Sharron Rayner, divorced, and director of a commodity trading company, dropped her childhood Mormonism long ago, but developed a general interest in religion. She began learning Hebrew as a cultural pastime two years ago. Now she is reading for an MA in Jewish studies and attending conversion classes. She intends to complete the process, along with her two children, in a few months' time.
The conversion game is not, of course, all sweetness and light. Even though Romain reckons, on the credit side, that individuals benefit as religion increases their sense of personal worth and promotes commitment to community involvement, he admits to negative factors. The brain-washing or "love-bombing" tactics of some new fringe cults put them at odds with what he finds acceptable. And he has found many instances of families torn apart when one member changes spiritual allegiance.
Mainstream religions are not blameless either. In Judaism, says Romain, it is still the case that most rabbis regard converts as unwanted intrusions. And the warm welcome in a conversion class is not always matched when the newcomer joins the congregation for regular services. Christians who join a synagogue might meet a coolness from some who feel they're not "real" Jews.
There can also be a difficult racial and cultural divide for anyone espousing Islam. Romain remarks: "A high percentage of white converts to Islam are middle-class, well-educated and professional. They have to integrate into a culture that is often lower class, poorer, and less educated."
Realising the difficulties that some new adherents face, support groups to help them have been set up in Islam and Judaism. The problem with this, Romain acknowledges, is that mixing only with fellow converts can slow the process of integration for new members.
At worst, such special attention may cause the majority of a mosque, temple or synagogue to brand new members as "exclusive". And if that sounds just a bit like behaviour at the local golf club, perhaps it helps explain why so many organised religions have been in so much of a decline.
Your God Shall Be My God is published next Monday by SCM Press at £12.95
Faith's top of the pops
Whichever way you look at it, the established Christian churches are in decline. But other religions are gaining ground.
According to Religious Trends, produced by the Christian Research group, combined membership of Christian churches is now less than 6m, or 12% of the population. It was 22% in 1970 and 31% in 1920.
The Christian "community" - defined broadly as those who have been baptised - is now put at 64% of the population, compared to 72% in 1970 and 84% in 1920. If other faiths are added, however, "all religions" repre sentation has fallen far less steeply in the recent past, from 75% in 1970 to 71% today.
Among the traditional churches, membership peaked in 1905 for the Baptists, 1910 for the Methodists, 1930 for the Anglicans, 1935 for Presbyterians and 1960 for Catholics. The only category to buck the downward trend for Christianity has been "others" - including Orthodox, Pentecostal and "new" or "house" churches - which has risen to a record combined membership of 908,000, from 678,000 in 1980 and a previous peak of 854,000 in 1930.
The number of active members of other religions is estimated at 1.5m. This is double the total in 1980 and more than three times that in 1970.
By far the fastest growing faith is Islam, with 675,000 active members compared to 495,000 in 1990 and 306,000 in 1980. There are now easily more Muslims than Methodists and Baptists put together. The number of mosques has risen more sharply still, to 660 today from 350 in 1990 and just 193 in 1980.
There are now 400,000 active Sikhs, compared to 250,000 in 1990 and 150,000 in 1980, and 165,000 Hindus, up more slowly from 140,000 in 1990 and 120,000 in 1980.
Like Christianity, however, the Jewish faith seems to be in decline. It counts its following as 88,800 heads of households, compared to 101,000 in 1990 and 130,000 in 1960. The number of synagogues is also down, although the number of distinct congregations using them is up.
Among more exotic groups, Religious Trends counts an estimated 5,000 Pagans, 2,500 Zoroastrians and 420 Satanists.
David Brindle