On average, the authorities spent between pound;33,750 and pound;37,083 on the visit from the Office for Standards in Education. Just over half of the 30 surveyed were unable to estimate costs - in part, because the additional work was absorbed by existing staff, often working extra hours unpaid.

“People did it on top of their usual jobs” - the response from Warwickshire - was typical.

Simon Bird, of The Education Network, an information service funded by local councils, said: “People tend to work longer hours. The figures provided (by education authorities) are fairly conservative because of this.”

The TES asked 30 of the 48 authorities inspectedby OFSTED since 1998 about their preparation costs. Seventeen could give no figures while several others could not account for officer time - the biggest expense. There seemed little relation between authority size and costs. Durham gave the fullest response, estimating that the entire OFSTED process - including post-inspection action planning - will cost around pound;250,000, mainly through officer time.

Surrey spent pound;37,000 on consultants, in addition to unspecified officer hours and paperwork. Kent, a huge authority with 104 secondaries, gave an officer time figure of around pound;50,000. That compared to a figures of between pound;50,000-75,000 at Middlesbrough, with 11 secondaries.

“We all did it working until 9pm at night,” said an education officer from Rutland.