Teachers are becoming drug addicts and developing eating disorders because the stress of the job is too much, a union warned today.

Excessive demands from ministers and management "bullying" have led to up to one in three teachers experiencing mental health problems, the National Union of Teachers said.

In an emotional debate at the NUT’s annual conference in Harrogate, North Yorkshire, delegates described breaking down in tears at school and warned that some colleagues, unable to cope, had taken their own lives.

A snapshot survey of 140 teachers in Nottingham found one in three "resort to alcohol, smoking, unhealthy eating or other substances to help them cope".

Magenta Stonestreet, a teacher from North Tyneside, described how she had struggled with depression and had to take four months off through illness because the pressures of work were so great.

"One of the things which I think was good is that I managed to get the kids out of the classroom the other day before I cried," she said. The union unanimously passed a motion which warned that severe mental illness can "shatter" the lives of teachers and their families.

"The types and causes of mental illness are complex but depression and acute anxiety are common amongst teachers," the motion said. "It is a major cause of teacher absence and many teachers are only able to continue working because of long-term medication.

"Drug addiction, eating disorders and obsessive behaviours are also common."

The motion was proposed by former NUT president John Illingworth, who won a standing ovation at last year’s conference when he broke down as he described how stress and "Government bullying" forced him to quit.

During the past year, Mr Illingworth, from Nottingham, has been campaigning on the issue of teachers’ mental health. He told the conference that he had received letters from teachers who had suffered similar problems.

One letter was from the wife of a headteacher who became depressed after a critical school inspection. Reading from the letter, Mr Illingworth told the conference the headteacher did not want to give up the job because he wanted to prove himself again.

"‘He never believed he was any good any more. Eventually after many bad nights of screaming and shaking he gave up and could not get out of bed to go to work. He retired six months later.

"‘He was a complete mental mess’," the letter said. "‘The day his job was filled I now see he had given up on life altogether.

"‘Two months later he ended it."’

Fighting back tears, Mr Illingworth said: "That is why this is important."

Patrick Nash, chief executive of the Teacher Support Network, said 37% of callers to the group’s helpline in the past year had expressed feelings of stress, anxiety or depression.