It’s not quite an ordinary day, but when you’re used to great occasions of state, a service commemorating the anniversary of the death of one queen and the accession of another isn’t going to throw you off your stride. Just an hour earlier, the boys, already wearing their scarlet cloaks and white ruffs, are in a rehearsal room sight-reading the Latin plainsong that will shortly accompany the procession into the abbey. Soon afterwards, the boys will be singing beside the tomb where the two queens lie side by side.

It’s days like these that make Westminster Abbey Choir School such an unusual experience for its pupils, says Jonathan Milton, the headmaster. Even among choir schools it stands out: in most choir schools, the choristers are in a minority, the abbey school is the only one solely for choristers.

As a result, it is small, just 33 boys, of whom 27 are singing in tonight’s evensong to mark 450 years since Elizabeth I succeeded Mary. The younger choristers are the ones to miss out, given lighter duties in their first year.

Boys join the school at eight. By the time they leave five years later, they will be well-used to singing in front of royals and statesmen in a setting that is the centre for many national occasions. They will have recorded CDs and been feted around the world as celebrated exponents of an art-form in which Britain’s reputation rides high. And if their timing is right, they may well have sung at a royal wedding or two.

The prospects for feeling intimidated seem limitless, but the boys are unfazed. “They take it for granted,” says Jonathan. “They think: `This is what we do’. It is quite a responsibility, but they’re proud of it and not daunted.”

About 20 children audition for the six or so places on offer each year. Although the boys need a good ear, James O’Donnell, the abbey’s organist and Master of Choristers, says he’s looking for more than just musical ability.

“The ability to be part of a team is important,” he says. “You have to have a heightened team spirit in a choir, particularly such a hard-working one as this.”

Even with the bulk of the costs met by the Dean and Chapter, who run the abbey, fees still work out at Pounds 5,600 a year. Bursaries of up to the full amount are available, and Jonathan insists no boy would be turned away if his parents couldn’t afford it.

As well as their singing potential and enthusiasm for music, the boys also need to be able to cope with life in such a small community. With just half a dozen boys in each year group, it’s important to be able to form close friendships. “It’s not to say that they’re all incredibly gregarious or in a particular mould,” says Jonathan. “Many of them like their own space and it’s important they allow each other space.”

That can be difficult, particularly when the boys live as well as work in the school. Although most come from within the M25, the choir’s regime requires all the boys to be boarders, with teddy bears jostling with electric guitars and football posters for space in the dormitories. Sunday services mean only the first years (Year 4s) go home for weekends, although the rest of the boys are free to spend Saturday and Sunday afternoons with their parents.

The school day begins with choir practice and ends with another practice followed by evensong, but in between the boys follow a standard independent school curriculum: English, maths, separate sciences, history, geography, ICT, French and art, plus Latin, and the option of Ancient Greek in their final year. Music practice - all the boys play the piano plus one other instrument - is timetabled into the day.

Jonathan says one advantage of being such a small school is that it’s easier to pick up if the boys are getting tired and adjust the routine accordingly. Six in a class - and sometimes fewer - also means the boys get more attention from their teachers, with less need for homework. There are 12 teachers - eight full-time equivalents - with four living in. That, plus the two matrons, makes it easier to spot any problems, such as homesickness.

As well as the regular services, there are numerous annual or one-off commemorations and celebrations, from Commonwealth Day and the Children of Courage service, to the 60th anniversary of the NHS. It’s a tough schedule, but the boys seem undaunted. “When you’re doing it, it doesn’t feel too much,” says David Warren, 12, from Croydon, south London.

Not surprisingly, Christmas is one of the busiest times of the year, a hectic round of services culminating in a carol service and midnight mass on Christmas Eve, then another service on Christmas morning. The boys are free to go home after lunch from 4pm.

The lower two years are excused Christmas duties, but the older choristers back up their headmaster’s claim that it is probably harder for the parents than for the boys still at school in the run-up to Christmas. “Christmas is the highlight of the year,” says Beans Balawi, 11, from Hampstead in north London. “There are so many activities, the music is really good and we get to decorate our cubicles in our dormitories.

“It’s different every year and there’s not really time to think about home. You don’t really get homesick because you’re having so much fun all the time.”

Beans says he loves the boarding life, but Jonathan acknowledges that the school has to work hard at it. Living in such a rarefied atmosphere and in such a small community could easily become claustrophobic.

The school takes up a just a small segment of the buildings on Dean’s Yard, surrounding a tranquil patch of green just behind the abbey. It may be just yards from the bustle of Parliament Square, but the opportunities to see new faces - at least outside the congregation - are limited.

“It could be isolating, so it is really important that they get out of Dean’s Yard,” says Jonathan. Out of school activities are arranged every Wednesday evening. Not surprisingly, concerts are a popular option, and the upside of living in central London is there’s no shortage of curriculum-enhancing trips available.

Although the school aims to provide places regardless of background, most boys go into fee-paying schools, many on music scholarships, when they leave at 13 - Eton and Harrow make regular appearances on the roll of honour in the music room. Part of the reason, Jonathan suggests, is that it is easier to transfer to a school where all the other pupils start at the same age, rather than one when everyone else will have started at 11.

He says few of the boys are anxious about moving to a larger school, or about no longer being seen as part of such an elite group. In any case, by that stage many of the boys are starting to shift attention from their singing to their orchestral instrument, no doubt helped by the looming prospect of their voice breaking.

There’s no telling when this will happen and for some of the boys it is while they’re still at the school. This year, the first voice to go belonged to Gus Streeting, the school’s head boy. He stopped singing a couple of weeks ago and formally lost his place in the choir the day before the service for queens Mary and Elizabeth. “It was strange to start with. It’s something I’ve done so much for the past four or five years, and suddenly I’m not doing it any more,” says Gus, 12, from Norfolk.

The school goes to great lengths to try to make boys in this position feel included - turning pages for the organist, helping organise rehearsals - but it can be hard to feel involved when so much of school life revolves around the choir. One tactic is to make sure the boy’s newfound free time is well-used, often in practising their instrument, cello in Gus’s case.

“Now there’s two hours or so every day when no one else is here, so I can practise or catch up on something I missed out on,” says Gus. “You don’t have time to feel left out.”

Even though the school is dedicated to something that has only a finite life, a choirboy’s voice, Jonathan says it is an experience that will stay with them. “Most will carry on with their music, some of them will have a career out of it, but it will always be an important part of their lives.

“They’re exposed to such a breadth of culture and they absorb it almost without knowing they’re absorbing it. We live in a privileged environment, but it is elitist in the right sense, offering something of amazing quality. That strikes me as very exciting.”