CCTV monitors classrooms at one in 14 schools, according to a survey.

The poll of teachers also found that almost a quarter feared there might be more cameras hidden around the campus that they did not know about.

Most said their schools were fitted with surveillance cameras. Almost 80 per cent said there were cameras at the entrance and more than 7 per cent said there were some in classrooms.

Nearly 10 per cent of teachers polled by the Association of Teachers and Lecturers said there were cameras in the lavatories.

Teaching unions said the cameras were being used to monitor pupils' behaviour. But they fear the devices could inhibit teachers from performing to the best of their abilities.

Supporters of the surveillance say it is there to protect children and staff.

Dr Mary Bousted, general secretary of the Association, said there were no rules governing the installation of the cameras or the use of images. 'No one really knows enough about the use of CCTV in schools  -  it's a very new issue.

'Certainly we would want staff to be involved in decisions about the use of CCTV in schools, and strict safeguards for its use. Although surveillance in schools can have some positive outcomes, such as discouraging vandalism and violence, we think there are some instances where it should be strictly controlled.'