Boarding school heads furious at being "overcharged" for their Ofsted inspections have won a battle to have the watchdog's fees slashed.
Mounting pressure from schools has led Ofsted to cut the annual fees that boarding schools now have to pay for their three-yearly inspection.
Several schools were so outraged by the charges they even refused to pay. A school of 800-plus boarders that was paying #163;13,123 a year to call in the inspectors will now face a bill of just #163;2,186.
More than 40 boarding schools which have more than 500 boarders will have costs reduced from #163;8,779 a year to #163;1,789. Around 32 state boarding schools have also been paying high fees for inspections.
The huge sums date from inspections by the now defunct Commission for Social Care Inspection.
The fees were justified on the grounds that schools received advice and support on how to comply with the law and run their boarding houses, a service which Ofsted does not offer.
Under the new Ofsted regime, which began in April 2007, heads started to question the levy and made a Freedom of Information Act request to find out the justification of the cost.
But this November, an amendment was made to the law lowering the charge and recognising that schools get a significantly reduced service from Ofsted.
No reimbursements will be paid to compensate for previous years' overcharging, but a reduced fee has been proposed for schools that have already paid this year's bills.
Melvyn Roffe, head of Wymondham College in Norfolk, the largest state boarding school, said it had been charged #163;21,000 over three years for a single day-long inspection with two inspectors.
He was among half a dozen heads who refused to pay the fees until the system was changed.
He said: "The support and advice services offered under the old system started to drop away towards the end of 2006, so we have effectively been overcharged since then.
"Nobody was ever happy with the fees, but we could rationalise them because we were receiving other services. But when we lost that, heads started to ask why the fees were so high.
"We knew they couldn't sue us for not paying because we knew the real cost to Ofsted of the inspection and they couldn't justify it."
Simon Davies, headmaster of the elite Eastbourne College, which has more than 300 boarders, has not paid the inspection fees for two years.
He said: "I refused to pay on the basis that if it was a tax they should tell me, and if it was a service they should tell me what I was entitled to."
Hilary Moriarty, director of the Boarding Schools' Association, said: "When you are confronted with a bill of #163;24,000 for an inspection, you start to think 'this can't be right, can it?'."
She said no one knew why the fees were so high before, but many had wrongly assumed private schools were overcharged to cover costs in other areas of the inspectorate.
"But actually the fees had just become seriously out of kilter with what the schools were receiving.
"In these recessionary times there is an every penny counts attitude, so it's wonderful news for all boarding schools."
A government memo explaining the changes to the fees said Ofsted had been able to set the new prices following an "organisation-wide efficiency review" which revealed the true cost of inspections.
An Ofsted spokeswoman said: "Fees payable by a variety of social care providers have been reduced. This followed an Ofsted review that established a model for inspection fees that, in the case of boarding inspection, reflects the actual cost of undertaking the inspection.