From the gothic chill of Chartres cathedral to the gothic charm of Johnny Depp in the film Sleepy Hollow, boys from the London Oratory have provided a choral backdrop. The younger ones, though, must wait to see the results of their labours, since Tim Burton’s Hammer Horror homage - in which Depp plays an 18th-century detective in search of a headless horseman - has a 15 certificate.

The choir, called the Schola, can also be heard on the soundtrack to The Miracle Maker, an animated life of Jesus which includes the voices of Ralph Fiennes as Christ and Miranda Richardson as Mary Magdalene. One of the Schola boys, 13-year-old Nicolas Santos, recently appeared on BBC1‘s Songs of Praise, performing the film’s specially penned Pie Jesu.

At half-term, posters in cafes and bars in Paris, Versailles and Chartres advertised a Schola tour which included Marcel Dupre’s vespers, and music by William Byrd and Thomas Tallis, and ended with a visit to Disneyland Paris for the boys. Several of them are this month performing in Martinu’s The Greek Passion at London’s Royal Opera House. Not bad going for an outfit set up from scratch less than four years ago.

Headteacher John McIntosh was in the vanguard of the grant-maintained movement; his school opted out in September 1989. Seven years later he confirmed his maverick reputation when he persuaded the Conservative government to give him a grant to set up a “junior house” ofboys aged seven to 10, in classes of 20, for specialist music education. The London Oratory now has 1,400 pupils aged seven to 18 and is voluntary-aided. Its main claim to fame is that Tony and Cherie Blair chose it for their sons’ secondary schooling - a controversial choice because of its grant-maintained status.

The junior house boys perform with professional singers who are members of the Brompton Oratory Church Choir - probably the poshest Catholic church in London’s Knightsbridge. In line with the Oratory’s general admission policy, pupils must be able to prove they are practising Catholics.

Musical director Michael McCarthy admits it takes a bit of crystal ball-gazing to spot vocal talent at such a tender age. He recalls the choir’s first rehearsal as “the most primitive” he’s ever taken part in - an incredible amount of raw talent, yet some boys “hardly knew their way round a hymn book, couldn’t read music and had never sung in a choir”.

Now, with its reputation firmly established, the Schola funds activities from ticket sales and sponsorship, and makes about pound;5,000 a year from commercial work. “Singing for our supper is what we do,” Mr McCarthy says. Other projects have included providing part of the musical background for the 1998 film American History X, which proved a rather less saintly venture. “It turned out to be a horribly violent film,” says Mr McCarthy. “Obviously the boys didn’t see any of it.”

A “back row” of professional adults - basses, tenors and altos, all on Equity rates - accompanies the choir on tour. Then there are the senior Oratory pupils, who can join the Schola when their voices have settled down. The boys learn a lot from working with the professionals, but even the tiniest treble enjoys parity with the oldest bass as part of the whole choir’s sound.

Being part of the Schola requires huge commitment from the boys and their families. The school day starts at 8am with voice practice, and boys sing in assembly 40 minutes later. After school, pupils are expected to rehearse on top of an hour’s homework. The Schola boys must also sing during evening Mass at the Brompton Oratory every Saturday in term time. “It can be a tough schedule, but droppig out has been no problem so far,” says Mr McCarthy.

Described by the Choir Schools’ Association as a “one-off”, the Oratory, unlike the majority of choir schools, is neither fee-paying nor boarding. Junior house boys are tested on entry to show they are “of at least average general ability” and have some musical aptitude, and in the case of would-be choristers, choral aptitude. They receive free tuition on one instrument and are expected to learn a second. Voice training is also provided. About six boys from each year will be chosen for the Schola.

“It is a heavy workload,” says Isobel Delap, acting head of the junior house. “The boys have a subject-based timetable and learn Latin and Italian. They arrive early and use the computers or practise their instruments. After lessons, the choristers will do singing practice and the others will join the various wind ensembles, string quartets and guitar groups they belong to. They will all also be studying for music exams.” A recent inspectors’ visit appeared to look favourably upon the junior house, even though it found no trace of the literacy or numeracy hours.

The Oratory’s central location, in the London borough of Hammersmith and Fulham, provides it with a ready pool of musicians, many from top orchestras, looking to supplement their wages by providing tuition. Mr McCarthy is a seasoned and much-recorded professional singer who has worked with, among others, the Tavener and Monteverdi choirs. Many of the staff are musical and put in extra hours taking part in concerts and accompanying school plays. The junior house has 10 air-conditioned music practice rooms, and is situated next to the school’s arts centre, which has a 340-seat theatre - opened in 1991 by the then prime minister, John Major - that most schools would kill for.

But the investment (some may say privilege) has paid off. This term’s sixth-form production of The Marriage of Figaro and the junior house’s In Quest of Columbus were slick productions, with bouquets and bows all round.

The junior house uniform, with its stripey blazer and cap (pound;107 from Sloane Square’s Peter Jones), is very prep school. But Sylvie and Richard Boden, parents of Schola boys, say the school avoids the elitism associated with most private choir schools.

As TV producers (Richard worked on the last Blackadder series), they admit they fit the bill as archetypal middle-class parents benefiting from the Oratory (another parent is a world-famous conductor). “This is a trailblazing school,” says Richard. “Very few can take boys from the age of seven to 18. It is strict, but it is also caring. The boys come from a wide range of backgrounds, and as well as music there is a lot of sport. They are just normal boys who pack away their PlayStations and Nintendos and pull on their robes to sing.”

Sylvie adds: “The Schola is just one part of a normal state school, bringing liturgical music to a wider audience and a wider range of children.”

So how can the school afford to do what it does? Initially, as a first-phase grant-maintained school, the London Oratory was the beneficiary of government grants and so-called “double funding”.

Some would say that when Mr McIntosh blamed a pound;250,000 deficit on the transfer from GM status back to the local authority fold he may have been masking his ambitious provisions for the school. The budget shortfall prompted a letter to parents asking for a monthly covenant of pound;30 - which proved an embarrassment to Tony Blair as it came on the eve of last year’s Labour Party conference.The school was also bailed out by a loan from the council.

After Mass on Saturdays the Schola boys rattle their collections boxes as the congregation leaves - presumably every contribution helps.