Dulwich college this week joined a growing band of private schools forming links with state education by sponsoring an academy.
At least 13 of the independently-run state schools enjoy sponsorship from fee-paying schools or organisations such as Global Management Systems, which fund private education.
Dulwich's announcement came days before the publication yesterday of the draft Charities Bill, which was expected to put pressure on private schools to show their benefit to the public.
But Graham Able, Dulwich's head, denied the decision to sponsor an academy in east London was a cynical attempt to protect its charitable status.
Other private schools backing academies are North London Collegiate in Edgware, London, King's in Canterbury, and Oundle, near Peterborough.