Historic King's School in Ely, Cambridgeshire, has warned that it may have to cut back its 1,000-year-old ties with the neighbouring cathedral if tax breaks for independent schools are redrawn.
The traditional musical connections could be severely curtailed, the headteacher says, if the Charity Commission redefines what fee-paying schools have to do to maintain their charitable status.
King's is one of the oldest schools in England, having been founded in a monastery in 970AD. Edward the Confessor was taught there.
The school's 40 choristers - boys and, more recently, girls - sing evensong every night at Ely Cathedral. The choir has also sung with less traditional groups, such as the King's Singers, an a cappella vocal ensemble named after King's College, Cambridge, and the Choirboys, a choral boy band.
The school's choir holds money-raising concerts for the cathedral which, like many, struggles for funds. And, once a week, pupils go out on a community service programme, helping in church groups and care homes.
A senior school boarding place can cost up to pound;20,000 a year, but a bursary to help cover the fees is awarded to many of the boys and girls whose voices show promise.
Now, the school warns that it may no longer be able to discriminate on musical grounds when it awards bursaries.
The Charity Commission is soon to finalise guidance that, as it stands, could force private schools to offer more means-tested bursaries to local children whose parents cannot afford the fees, regardless of academic, sporting or musical merit.
King's School has written to the Charity Commission, asking that its good works in the cathedral and the community be acknowledged as a public benefit.
Sue Freestone, the headteacher, said that if the definition of "public benefit" were narrowed, the school would have to scrutinise all its bursarial giving.
"The core of the school's being is its 1,000-year relationship with the cathedral," she said. "But supporting the cathedral music is no longer part of the Charity Commission definition, and that may change the very nature of the school.
"The choirs may become more exclusive, because they will be the domain of those singers who can afford the school fees."
Independents' threat, pages 16-17.