How many of Britain's cherubic choirboys do you think are actually cherubic choirgirls? The answer may surprise you, for in the 44 choirs affiliated to the Choir Schools' Assocation - mostly cathedral foundations and college choirs - more than a quarter of choristers (27 per cent) are now female. What's more, the number of female choristers has more than tripled in ten years. As the nation's worshippers settle down in the pews this Easter, it's never been more likely that the pure treble sound ringing out to greet them will be coming from this influx of female talent.

A gentle revolution it may be, but it is inspiring a passionate debate across the country, in congregations where the sound (or, perhaps, sight) of mop-headed boys in cassocks is considered quintessentially English. “Indisputably, a lot of the greatest music written for English cathedral choirs was written for boys,” says David Halls, the director of music at Salisbury Cathedral, “and that adds some weight to a boys' tradition worth preserving.” Yes, Halls also directs a separate (and widely praised) girls' choir, but like so many working at British cathedrals, he knows that the future of the boys' tradition is not guaranteed.

Yet in the church where this revolution began 30 years ago, feathers remain unruffled. In 1978, eight-year-old Susan Hamilton made history when she was accepted into the choir of St Mary's Episcopal Cathedral, Edinburgh - a choir that has remained mixed ever since. Now she is a founder-member of the Dunedin Consort, who have just released an acclaimed recording of Bach's Matthew Passion (see review, page 17). She joins them and St Mary's Choir for a performance of Bach's John Passion on Wednesday. “It was a very dramatic change,” she admits, “but I am where I am today because I got the chance of this education.”

Hamilton is certainly not the only woman to have ascended from the ranks of girl-friendly church choirs to a glitzy professional career. The fresh-faced star of Kenneth Branagh's recent Magic Flute film, Amy Carson, is a product of Halls's girls choir in Salisbury. Now 24, she was also one of the very first girls to join, back in 1992. “I value it above any other experience since. We were making music every day, but also developing the other things that come with making music, like teamwork.”

All good for equal rights, but what is the real future for boys' singing when there is now so much competition? “Well, it's disappeared, hasn't it?” says Edward Higginbottom, the formidable director of music at New College, Oxford, where the all-male tradition goes back to the 14th century. “In parish churches these choirs have gone altogether.” His concern is not just the disappearing boy trebles, but that ex-choristers who would otherwise have joined choirs as men, in the bass, tenor or alto lines, will simply not have the experience or inclination to do so.

Higginbottom is not casting his pessimistic gaze over the cathedral choirs - yet. Although he bridles at the idea of “pressure against an institution because it's not representative”, he calls the decisions to admit girls in Salisbury, Wells, Winchester and elsewhere “irreversible and quite proper”. Neither is he among those who argue that a girl's voice is less appealing than a boy's.

But he is adamant that the battles need to be fought to safeguard the boys-only treble line. “The only way we can get boys to sing is to get them to sing []as boys[]. You have to make an accommodation with what boys are likely to want to do, and that's where I think you can fall into difficulties with not reading enough into particular gender needs.”

The result in mixed choirs such as St Mary's, Higginbottom claims, is that “a lot of girls are brought in to sing, and boys have walked away”. He also finds the notion of combining the girls and boys choirs (as happens in Salisbury for the big services) musically unappealing: “I have to know what my instrument is.”

Perhaps it is because these concerns are shared so widely that few cathedral choirs have followed St Mary's lead. In England, only Manchester Cathedral has a mixed choir. The others that have opened up their doors to girls divide their time between two single-sex choirs.

“Different institutions come up with different solutions to getting girls involved, but it can be a bit of a fudge,” says Duncan Ferguson, St Mary's acting organist and master of music. “If you're starting from the standpoint that it's good to give girls the opportunity to sing, either you go down the route St Mary's went down in 1978 - to create a mixed line - or a separate choir, which means either girls have a nominal amount to do, or you split the amount equally, then reducing what the boys do.”

Do the boys mind singing and socialising with girls? “It's a very pleasant working environment and I know that other members of the congregation find the same thing.” Nor does Ferguson have any truck with Halls's passion for preserving “authentic” performances of Purcell or Tallis with boys only. “Would composers have really written different music if they had had girls singing? It's far more important to have a choir that sings this music from the past pretty well.”

Making the gender split equal can be difficult. Ferguson admits that “there are periods in the year when the balance is not ideal”. “But we have been fortunate that we seem to be able to maintain that balance without compromising and rejecting people that are good enough. But, as with all cathedrals, recruitment is a major issue, and, going forward, maybe more of a problem finding boys than girls.”

That's something everyone can agree on. Yet, given that most children under 13 (when boys' voices usually break) are in co-ed schools, is dividing the sexes a logical answer?

According to Gareth Malone, choral campaigner and TV presenter: “Girls are totally up to the task and it's ridiculous to exclude them.” His second BBC series of The Choir has just screened, this time trying to build a choir in a gritty all-boys comprehensive in Leicester. “There are many reasons why the Church is struggling to get applications,” he adds, “and they are not all about boys singing.”

Although Malone does suspect that boys are less inclined to sing alongside girls, he thinks it's more important to recognise the growing disconnection between church choirs and today's children. “When I go into a school I have to declare: ‘We might have to do some religious music, does anyone mind?' It's the way of the world, and a difficult tide to fight against.”

So maybe these quarrelsome choirmasters should pay less attention to balancing the timbre of their trebles, and try harder to reach the boys and girls (and their parents) who might never think of choir singing at all.

“The challenge is trying to get people to come and see it and hear it,” Higginbottom concurs, “and not to be put off by the image of choirboys dressed up in pretty cassocks who are on another planet. But you only have to see it working to know that this is not about the preservation of some fossil. These are living organisms and we want to see them flourish.”

The Dunedin Consort perform the

St John Passion on Wed at St Mary's Cathedral, Edinburgh (0131-538 7766)

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