A school installed CCTV cameras in classrooms in a bid to avoid disputes between teachers and pupils and prevent theft, the deputy head said today.

Stockwell Park High School, in south London, is currently being rebuilt and as part of the overhaul a hi-tech surveillance system has been put in place.

So far there are cameras in 28 classrooms as well as corridors and stairwells, and there are 40 more outside.

Deputy headteacher Mike Rush envisages the number of cameras doubling when the rest of the building is complete.

He said: "It's been a gradual process. To begin with we had cameras just at the entrances and exits to the school because we had a problem with intruders coming onto the school site and harassing and robbing the children.

"They were very effective at stopping that problem. Once we had that positive experience with cameras, we were then in a situation where we were putting a lot of expensive equipment into the school and we wanted to protect it. So that was when we started to put cameras into the classrooms."

He insisted that the reaction from staff, children and parents had been entirely supportive.

Mr Rush said: "The children are very happy here because they know they are on a school site where they are safe. They are in a position where they are not going to be robbed and harassed and so on. The parents are very happy with it.

"We've had no complaints from the teachers about it being a Big Brother system watching them all the time.

"They were the ones who suggested the cameras as a solution to people coming into the building, and disputes and problems with theft."

He said that the cameras could be used to resolve disputes about bullying or if claims were made against teachers.

Access to the footage is tightly controlled, and those who wish to use it must apply to the principal in writing and only the facilities manager can give it to them, Mr Rush added.

The Association of Teachers and Lecturers said it was told about four schools in Salford, in Greater Manchester, which installed similar systems in March.

General Secretary Dr Mary Bousted said: "This all sounds very 'Big Brotherish'. We have major reservations about using CCTV to monitor staff. It would be hard to see how teachers would act naturally if they knew they might be being watched all the time on camera.

"And it sounds as though this goes against what's been agreed in the social partnership for teachers to be monitored for a maximum of three hours in any school year. Schools should not have to resort to technology to fight bullying and bad behaviour.

"And what happens if an incident occurs in an area hidden from the cameras? CCTV can be useful to monitor outside areas to ensure strangers do not enter schools, and may help cut down on vandalism, but we have grave concerns about using it as panacea for all the problems a school faces.

"We would certainly want staff to be involved in decisions about the use of CCTV in schools, and be strict safeguards for its use."

Chris Keates, General Secretary of teachers' union the NASUWT, said cameras were inappropriate and a waste of money.

She said: "We do not support the use of cameras in this way and see no professional security or educational benefits to such systems.

"More and more schools are wasting thousands of pounds of taxpayers' money on CCTV cameras which all available evidence shows are not the most effective method of maintaining school security, neither are they an appropriate way of monitoring classroom practice."

General Secretary of the National Union of Teachers, Christine Blower, said the surveillance set a "worrying precedent".

She said: "Schools must have the right to make their own judgments on security issues, but there is a danger of becoming over-zealous in the use of CCTV to tackle pupil behaviour. Of great concern is the potential for covert surveillance of pupils and staff.

"Certainly, the use of cameras within the classroom is not appropriate and sets a worrying precedent. Any school system must be totally transparent and recordings must never be used for monitoring of staff. Teachers are assessed often enough and, importantly, within the law."