The action follows last year’s industrial tribunal victory for Wirral teacer Muriel Benson who was awarded pound;47,000 after being forced to leave her job due to stress.

National Union of Teachers general secretary Doug McAvoy said more cases were in the pipeline, 30 in advanced stages, which would give significant awards to teachers.

Delegates heard that a recent Bradford survey found that nearly 60 per cent of teachrs were suffering from stress requiring medical attention.

Executive member Simon Jones claimed one in four teachers had been subjected to bullying at work and said that the headteachers responsible should be held to account.

Mr McAvoy later told journalists that where bullying headteachers or heads of department ignored teachers’ concerns, members could ballot to refuse to work under them. The union has produced a booklet, Tackling Stress, for teachers which will be sent to schools this month.