Her recordings include scenes in which pupils tell her to “fuck off”, a boy tells her to “suck me off” and students punch each other.

Channel 5 hopes to broadcast a documentary containing the footage next week, but fears it may be forced to cancel the programme if the secondary schools or local authorities take out an injunction.

The teacher, who uses the pseudonym Sylvia Thomas, used tiny cameras hidden in a briefcase and a button on her jacket to film lessons in around 15 schools in London and the north of England over three months.

She is in her late 50s and decided to approach a documentary-maker shortly after returning to teaching last year after a 30-year gap.

On one of her first days she witnessed fights, saw a student downloading pornography on his mobile phone during a lesson, and had classroom chairs smashed apart by angry pupils.

“I sobbed my eyes out,” she said. “I thought maybe it was because I was a bad teacher, or because I was on supply. But I’ve shown the video to teacher friends and they say the same things have happened to them.”

She was shocked most by the allegations of abuse. “The video shows me trying to stop a group leaving the classroom by standing in front of the door.

One pupil says ‘You have just touched me’ even though it is very clear I did not.”

Ms Thomas said the schools were chosen by her supply agency and that she had not deliberately picked any because their behaviour was especially poor. She is not teaching now.

Classroom Chaos is on Channel 5 on Wednesday at 8pm.