About 80 buses have been fitted with digital cameras funded by the county council at �2,000 per single-decker and �2,500 per double-decker.

In some cases the cameras have caught images unrelated to school pupils which are being used in police inquiries.

The installation of the devices began two years ago and is part of the ongoing "Respect for Transport" scheme.

'Clear evidence'

Nottinghamshire County Council, which joined the project last year, initially fitted analogue cameras but fitted digital ones when the original ones proved too limiting.

Bus drivers have also reported improvements in pupils' behaviour and are more confident action will be taken over incidents because of camera evidence.

The authority's bus services manager Andy Buckland said: "Not all the cases (of bad behaviour) are necessarily ones where school children are the culprits. Some may involve the misbehaviour of other people."

He added that the cameras could help parents.

"If their child is accused of doing something, then there is clear evidence that any action taken is justified."