The Office for Standards in Education has abruptly terminated the contracts of the primary heads and deputies who were taken out of their schools to work as additional inspectors as recently as last month. This was to make up for OFSTED’s crisis shortage of primary inspectors.

Primary schools have been astonished to learn they must now accommodate the returning staff. They have to demote teachers standing in as heads and deputies, cut their salaries, and sack any outside help.

The result, say the teaching unions, could be serious financial embarrassment. The National Association of Head Teachers has demanded compensation for any schools who are hit.

Some heads had even resigned from their jobs on the promise of work as additional inspectors.

Meanwhile, successful secondary schools which had not been expecting a visit from OFSTED for another four years - under the new six-year cycle - have been told they must prepare for a September inspection in the interests of a “balanced” sample. This is even though they were inspected within the last two years. The Secondary Heads Association described the development as “confusing and disturbing” and has written to OFSTED seeking an explanation.

Some 240 additional inspectors this week received an apologetic letter cutting short their year-long contracts. Those due to work until August will finish in May; AIs expecting to finish in December will stop at the end of August.

“OFSTED very much regrets having to take this action and appreciates the considerable disappointment and anxiety it will create,” it says, “not just for individuals, but in some cases for the schools from which they are seconded. ”

The news has been condemned by the teaching unions. “One can only ask if this is a satisfactory approach to running a school system,” said John Bangs, of the National Union of Teachers. “OFSTED really has to consider its responsibilities.”

“It will cause chaos,” said David Hart, general secretary of the National Association of Head Teachers. “OFSTED should have known there was a very real prospect that the contracts awarded for January this year would be terminated. ”

He said that schools are being badly treated, despite having rescued OFSTED from a crisis. “OFSTED were desperate to recruit additional inspectors to save their own face. They would otherwise have been well short of their target and it would have been significantly embarrassing for the chief inspector. He ought to bear in mind that he has left a lot of extremely angry and disappointed people.”

Nigel Goodall, head of Five Ashes primary school in East Sussex, said his school will face financial difficulty. “I have given out contracts on the strength of the AI scheme,” he said. “Now OFSTED is curtailing it thanks to its own miscalculation. It’s outrageous.”

An additional inspector who received the termination notice this week said, “we have worked our guts out to keep up with a difficult schedule. Then they turn round and do this. We feel very aggrieved.”

An OFSTED spokesman said the decision was taken “with a heavy heart”. But there are now enough private inspectors to handle the remaining school visits: OFSTED is legally obliged to use private contractors where possible.

“The AIs have done an extremely good job in helping us meet our targets, ” he said. “But in effect we have no more work for them.

“The law requires us to put contracts to the market first. Unfortunately we did not have confirmation that the market could cope on its own until December. ”