Andrew Halls, King’s College School’s headteacher in Wimbledon in London, claimed local lawyers, accountants and military officers had stopped sending their children to top independent schools due to the cost.
However, he claimed an “endless queue” of rich families from outside Britain had pushed up fees, but it was a “time-bomb” he likened to the financial crisis of 2008.
The 185-year-old school, named by The Sunday Times as the independent school of the year, charges about £20,000-a-year for boys aged seven to 18 and girls aged 16 to 18.
Mr Halls said: “We have allowed the apparently endless queue of wealthy families from across the world knocking at our doors to blind us to a simple truth: we charge too much.
“Somewhere along the way, first the nurses stopped sending children to us, then the policemen, the Armed Forces officers, then even the local accountants and lawyers.
“The most prestigious schools in the world teach children of the very wealthiest families in the world. We are in danger of coming across as greedy because we can charge what appears to be limitless fees, but in truth there is a fees time-bomb ticking away.”
Research found the cost of private schools has risen by about a fifth in four years – four times faster than rises in earnings.