In the end, John Illingworth was a physical and emotional wreck. After 24 years leading an inner-city primary school, the headteacher simply could not take the pressure any more.

“It reached the point where I couldn’t make decisions, couldn’t prioritise things and just started wandering around the school not knowing what I was doing or where I was going,” he said. “I started to be physically sick at school, I was not sleeping and I had an eating disorder. In short, I’d completely lost it.”

Mr Illingworth is among the record numbers of teachers who quit the profession in the last year, many of whom have blamed soaring stress levels.

New figures released by the Government this summer show that 13,790 teachers retired in 2004-05, the highest number since Labour came to power in 1997, when changes to the teachers’ pension scheme prompted a wave of early retirements.

Mr Illingworth, the 55-year-old former head of Bentinck primary, Nottingham, and a past president of the National Union of Teachers, has not worked for almost a year now. Last November he was ordered home on long-term sick leave and, last month, he formally retired on medical grounds having been diagnosed with an “adjustment disorder”, a combination of depression and severe anxiety. He will never work in a school again.

In April, he became something of a cause celebre among teachers when he broke down in tears while recounting his experiences of his leaving to the NUT annual Easter conference in Torquay.

“The response to the speech was overwhelming,” he says. “In the 24-hours after I made it, more than 100 delegates spoke to me and nearly all had similar stories to tell. I’ve been a head for 24 years and the job has got progressively more difficult.

“It has always been emotive, difficult, work, but in the past we had long holidays and a relatively short working day to recuperate. That’s not the case any more.

“Teachers now are working 53-hours or more a week, only half of which is in the classroom.

“They have to produce evidence for the school’s self-evaluation, required by Ofsted, they are observed more regularly, they are implementing initiative after initiative and are dealing with more difficult behaviour.

“My behaviour started to change probably five or six years ago, but I didn’t know things had got as bad as they did.

“In my school, apart from me, four other staff in the past five years have left teaching citing mental health issues and others have had time off.

“I was in group therapy with eight people who met every week. As time went by, I discovered five worked in schools. For a random group of people, I found that extraordinary.”

* graeme.paton@tes.co.uk