One in four headteachers will quit unless their spiralling workload is reduced, Britain’s biggest headteachers’ union will claim today.

The National Association of Head Teachers will complain that pressure on their members is now intolerable, partly because they have been so busy cutting the workload of classroom teachers.

Delegates at the association’s annual conference, which starts today in Harrogate, will hear that some primary heads now spend as much as four-and-a-half days a week teaching while hundreds of schools have been left without a permanent leader.

Mick Brookes, who attends for the first time as NAHT general secretary, may have promised that the conference “won’t be a moan-fest” but motions are dominated by fears about bureaucracy, workload and inspection.

The association will today publish the findings of a poll of 688 heads and deputies, carried out by Keele university. It indicates that 27 per cent will consider changing jobs if conditions do not change.

Most heads say their hours have increased since September when classroom teachers gained a guaranteed 10 per cent of their timetable free for planning, preparation and assessment (PPA).

Mike Welsh, head of Goddard Park primary in Wiltshire, will call for immediate action to reduce heads’ workload. “Neither I nor any of the heads I speak to have known anything like this pressure before,” he said. “The workload is so great it is affecting our health and our social lives - several colleagues in my region have retired because of illness and one has quit to become a lorry driver.”

Guidance issued last year stated that heads, even in smaller schools, should spend no more than half their timetable teaching.

Yet the NAHT survey found that two-thirds of heads were teaching regularly and that a third did not get the time they should to carry out leadership and management tasks.

Heads will complain that some schools are still trying to get them to teach pupils for more than half their timetable and are advertising posts which consist of 80 per cent teaching. Mr Brookes said that a Northumberland head had been forced to increase his teaching commitment from 70 to 90 per cent purely to ensure his staff got their guaranteed marking time.

“We are very good as headteachers at looking after everyone else, but not so good at looking after ourselves,” he said. “There is a culture of excessive hours.”

Heads who take lessons should also be given 10 per cent of their teaching time for planning and assessment. But the NAHT survey indicates that fourth-fifths get no PPA time at all.

All the heads surveyed said they had to cover for staff, with more than a fifth saying they spent between 41 and 100 hours a year filling in for other teachers.

The NAHT says that growing pressure on heads from the Government and from inspectors is discouraging teachers from applying for senior posts, leaving up to half a million children in schools without a permanent leader.

Responses to a survey from a selection of local authorities suggests that as many as 1,200 schools are operating without a permanent head although that figure is nearly double the one published last year by the Government.

Mr Brookes said: “The Government says there is no crisis, but it is in denial.”

The Government has refused to send any ministers to the conference. The NAHT pulled out of the workload agreement last year.

The one politician speaking will be David Willetts, shadow education spokesman. Mr Willetts will announce that the Conservatives will be trying to amend the new education Bill to make it an offence for newspapers to identify teachers who face criminal allegations unless they are found guilty.

“We know that teachers have suffered enormous distress and that their careers have been damaged by allegations that did not turn out to be true,”

he said.

Carole Whitty, the NAHT’s deputy general secretary and a former secondary head, will warn that schools have been trapped in a downward “hysterical spiral” since the introduction of school inspections in the 19th century.

However, despite the warnings of catastrophe, the conference has the upbeat theme of “Celebrating TLC”. Desmond Hamilton, who will become the association’s president tomorrow, said there were many interpretations of the initials, including “Teaching and Learning Creatively” and “Transforming Leadership Collegiately”.

Dr Hamilton, head of Strandtown primary in Belfast, said: “As school leaders we all need Tender Loving Care.”

* michael.shaw@tes.co.uk