Pupils at private prep schools are switching to state-funded boarding schools for secondary education to avoid high numbers of foreign students and to boost their chances of getting in to university, a leading headmaster has claimed.
Parents also wanted their children to experience a more diverse social mix and were increasingly reluctant to pay fees of up to pound;35,000 a year, said Paul Spencer-Ellis, chairman of the State Boarding Schools' Association.
Mr Spencer-Ellis, headmaster of the Royal Alexandra and Albert School in Surrey, said that when he became a headteacher in 2001 it was "pretty rare" to be contacted by a prep school about a pupil who wanted to apply, but now it was "very common".
Mr Spencer-Ellis was speaking ahead of his association's annual conference, which begins on Sunday at Holyport College, a new boarding free school in Berkshire backed by Eton College. He suggested parents were concerned that the increasingly high proportion of pupils in independent institutions who come from overseas were making schools feel less "British".
According to the Independent Schools Council's annual census, 24,391 non-British pupils whose parents live overseas are currently being educated at its schools. In recent years, many private schools have been forced to look to foreign markets as fewer domestic parents can afford to pay.
State boarding schools do educate European Union citizens but the number of international students is much smaller.
"There's a danger in the independent sector having too many overseas boarders," Mr Spencer-Ellis said. "It provides a rich community, but if it's a British boarding school experience that these overseas boarders are buying, at what point does it cease to be a British boarding school?"
He added: "I get a number of parents who do say to me - they get quite awkward when they say it - `the international dimension, headmaster, do you have many overseas students?' and I tell them the truth, I've got about 25. And that is quite clearly, to judge from the way that they act, the answer they want.Foreign students enrich the mix, I'm convinced of that, but I do wonder at what point it changes the nature of a school."
The headmaster, whose school charges full boarders pound;13,920 a year, revealed that he had experienced growing interest from prep schools. "Prep school headteachers ring me up and say: `Paul, I've got a delightful young child.whose parents are very interested in your school," he said.
"It may be that they could afford any independent school in the country, or it may be that they would struggle to pay pound;35,000 a year, but I think it's very interesting that parents say one of the advantages of our sector is the social mix."
Mr Spencer-Ellis added: "There is also a fear that if a child is at an independent school, they will be discriminated against by some universities. Some parents believe that and I suspect they are right in some cases."
Fees in the UK's 38 state boarding schools are relatively low: between about pound;9,000 and pound;14,000 a year. A recent report commissioned by stockbroker Killik and Co found that private school fees had risen 300 per cent over the past 24 years, although wages had risen by just 76 per cent.
"Independent boarding schools have priced themselves out of the traditional market," Mr Spencer-Ellis said. He added that one of his recent pupils would have been "fourth-generation Eton College", but had come to the Royal Alexandra and Albert School instead because of financial pressures.
Mr Spencer-Ellis also pointed to a recent survey of 1,500 parents with children at state boarding schools, which found that more than 80 per cent had chosen that route because of the schools' "high academic quality".
Jonathan Taylor, principal of Wymondham College in Norfolk, which has 700 boarders, said he had experienced a similar trend, with 10 per cent of the pupils joining in Year 7 and 9 now coming from prep schools. "What many parents have said to me is that their primary reason is the quality-to-cost comparison," he said.
He added that his school offered the same range of extracurricular activities as a private institution and had sent 12 pupils to Oxbridge this year. "You're getting a high-quality product at a significantly lower price," he said.
Barnaby Lenon, chairman of the Independent Schools Council, said he doubted parents would be put off by overseas students in association schools, where numbers were not allowed to become excessive.
He added: "The number of British students in UK independent boarding schools rose last year, suggesting that boarding remains popular. The financial pressures may be real, but the ever-improving success rate of independent schools in terms of university entry leaves no room for the theory that our pupils are being discriminated against."
Last year, the Good Schools Guide warned that "second-rate" UK private schools were packing their boarding houses with overseas pupils to fill a growing number of empty spaces.
Struggling schools have "houses full of mature Chinese pupils" who plug themselves into the internet and "refuse to join house activities", the directory says. It describes one school's dining room as "a babble of gambling cliques [that] could have been in Beijing".
The comments come amid concerns that some foreign parents are being misled when sending their children to school in the UK, expecting them to receive an authentic British education.
The guide points out that if the proportion of overseas pupils exceeds 20 per cent, the "British feel" - a principal selling point - will be compromised.