The Department for Education and Employment said that the abolition of the School Premises Regulations this week and their replacement with non-statutory guidelines on classroom and playground space will give schools greater flexibility. School governors and education authorities will still be able to set overall admission numbers, it said.

But the National Association of Head Teachers said that the move deprives heads of a crucial means of limiting admissions - and that some will be tempted to push class sizes to the limit.

The NAHT said that members have expressed fears that deregulation will endanger children’s health and safety.

The National Union of Teachers was also critical. “With the abolition of minimum space requirements schools have effectively lost all protection against overcrowding,” said a spokeswoman. “And it can only get worse because of pressure on schools to admit pupils in order to get funding.”

This year’s annual report by chief inspector Chris Woodhead estimated that at least one primary school in seven and one secondary school in five suffered from a shortfall in accommodation, and Government figures indicate that one-third of primary children in England were being taught in classes of more than 30, an increase of 9 per cent on last year. The survey by The TES published today (see page 6) suggests that this could be an underestimate.

Several schools have tried to limit the number of new pupils they enrol by using the minimum space regulations, which were laid down in 1981. One such is the Latchmere infant school in the London borough of Kingston-upon-Thames, which is stretched to capacity, with nine classes of 35 pupils.

According to the minimum space standards, the Latchmere should have 775 sq m of teaching space, but it has only 617 sq m - a shortfall equivalent to two classrooms. In May, the school’s governors, backed by their local education authority, decided to invoke the law on space per pupil to justify a reduction of intake to 30 per class.

The idea was abandoned after the school calculated that it would lose too much money, but the chair of governors, Caroline Egerton, said that she remained convinced of the value of the regulations. “They are the basis upon which you submit an appplication for funding,” she said. “Removing them effectively reduces our bargaining power.” This month she will meet schools minister Robin Squire to discuss class sizes and press for the reintroduction of legislation covering extreme cases.

The Labour party opposed abolition of the regulations and has promised to limit the number of pupils in an infant class to 30. But it has not made a similar pledge on older pupils.

Margaret Tulloch of the Campaign for the Advancement of State Education (CASE) said: “Labour should commit itself to the example set in Scotland where limits are placed on class sizes as part of teachers’ pay and conditions.”

Regulations covering playing fields will remain in place because, according to Mr Squire, schools and local authorities may be tempted to sell them off. But, he said last year, “that temptation does not arise in the same way in the case of teaching accommodation or recreation areas.”