Just when it seemed safe to go back into the classroom I letters arrived in schools heralding an unexpected early return by the inspectors.

The Office for Standards in Education wrote to more than 600 headteachers nationwide telling them that they had been selected for inspection - sometimes barely a year after the last.

John Dennis, head of Broadgreen comprehensive, Liverpool, said: “You can imagine the reaction when I told a staff meeting we could expect the inspectors in only 14 months since their last visit.”

The Liverpool experience was not unique. Letters went to schools in Cheshire, Buckinghamshire, the London borough of Haringey and many other local authorities, engendering panic and fury.

One head told The TES: “I got the letter on Friday, and spent the whole weekend wondering how I was going to break the news to my staff.”

OFSTED has admitted there had been a mistake. The computer program used to sort out the next inspection cycle had failed.

An OFSTED spokesman said: “We have sent out letters to a large number of schools saying we gave them the wrong date. But those who thought they could relax for the next four to six years, may still find they are being called up earlier than they expect.”

More than 600 of the wrongly-dated letters were sent in all, 554 to primaries, 54 to secondaries and nine to special schools.

Some of the schools have now been told they will not be inspected this academic year, and others that they will not be visited in the autumn term but will be notified of a later date.

But there is a catch. A select band of schools have learned that they are to be re-inspected with a gap of barely two years - and it is not a computer error.

The second inspection cycle has changed from four yearly to six yearly, although the intention had always been for an early follow-up of poorly performing schools.

However, because OFSTED needs an overall picture of national performance for the chief inspector’s annual report, a cross-section of other schools will have to be inspected as well. This means many schools could have a minimum gap of two years since their last inspectors’ visit. Alan Smithies, head of Speake community comprehensive, said that while he has been given his stay of execution, the revised date will mean a mere two-year gap between inspections. He said: “We have a four-year action plan based on our last inspection. I’m not sure there will be much more to see if we are visited so soon.”

Diary, page 19