Professor Duncan Lewis of Glamorgan said that 5 to 10 per cent of employees in most professions were exposed to bullying, at a social and economic cost to society.

In the summer term this year, 338 teachers lodged complaints of bullying with the helpline - a considerable increase on the 83 complaints for the same period last year.

TSN hopes to ascertain whether the rise in complaints was caused by worsening behaviour or greater willingness to report bullying.

Patrick Nash, the network’s chief executive, said that workplace bullying troubled increasing numbers of teachers and lecturers.

“The effects include stress, anxiety or trauma for the victim, a decline in emotional and physical well-being, sickness absence and, in extreme cases, resignation,” he said.

Denise McKeon, a Bournemouth secondary school teacher, spent long periods off work suffering stress and depression during two years in which she said colleagues shouted at her in front of pupils.

She won a financial settlement in 2005, after months taking the anti-depressant Prozac. She is now supply teaching, but still finds life hard.

“The stress from the way I was treated has changed me,” she said. “I only just function now. I find it difficult to complete simple chores in the home, feel tired and have no energy to focus on my children.

“It’s like breaking a leg. Stress makes you weak and you never really get the strength back.”

Bournemouth Borough Council said that bullying was not the reason for Ms McKeon’s departure.

Vicky Hughes, a council manager, said: “Had there been an allegation or complaint of bullying or similar conduct against anyone working in the school, management would have taken this seriously and investigated.”

www.teachersupport.info.