The survey, compiled by union officials in 25 local authorities in England and Wales, revealed that statutory dismissal warnings have been issued by 569 schools in the 6,129 sample. The union calculates that nationally at least 4,000 teachers could lose their jobs this year because of council budget cuts. A spokesman said: “It is a black picture. Although it is down on last year’s figure, it is very worrying to see so many posts being lost while pupil numbers are rising.”

Many of these posts will be lost through early retirement or voluntary redundancy, but the union says it expects a number of teachers to spend their summer holiday contemplating life on the dole queue.

Secondary schools will bear the brunt of the losses and, according to one official: “Most classes are at the upper limit in size. Any further staffing cuts will raise classes to over 40 in some primary schools and to 35 in some secondary schools.”

The survey also highlights the spread of part-time employment, particularly in the primary sector. “There is an increasing casualisation of the workforce, especially in primary schools, which mainly affects married women who are tied to their jobs because of family commitments,” said a spokesman.

The branch officials compiling the information discovered that schools are still informing union representatives of possible redundancies, despite recent legislation which means schools need not notify the unions in cases where fewer than 20 posts are threatened.

Peter Smith, ATL’s general secretary, said: “The feel-good factor for teachers and parents remains as elusive as ever. Job insecurity is bad enough, but equally worrying is the inevitable racking up again of class sizes this September. Once more teachers and parents are paying the price for continued underfunding and mismanagement at a time when they are told education has never been more important.”