Jean Webster, a Cornish primary supply teacher (pictured above), approaches schools direct to offer her services. “I refuse to use agencies because the huge profits they make are not going back to the children in the classroom,” she said.

Mrs Webster believes that the system has destroyed the old practice of “trying out” supply teachers to see if they are suitable for a permanent job. Agencies can demand a hefty “placement” fee if a supply teacher is offered a permanent post.

Robert Williams, a north Wales secondary supply teacher, also asks schools to contact him directly. “I was appalled at how supply teachers were exploited. In this area, they are paid on average pound;90, while agencies charge schools about pound;170 per day,” he said.

Mr Williams believes the lack of pension provision discriminates against women in particular, as they form the majority of supply teachers. “Many women don’t realise that they’re losing their pension rights,” he said.

Supply teachers employed by an LEA can opt to stay in the Teachers’ Pension Scheme.