Paul Stephens, operations manager of Avon, Somerset and Gloucestershire Safety Camera Partnership, said the level of abuse was getting "out of control".

He told BBC Radio 4's PM programme staff had been pelted with eggs and abused verbally.

"They're subjected to abuse, threats and obstructions several times a day each and every day.

"It's almost like the Chinese water torture - it's drip, drip, drip," he said.

Criminal prosecutions

Mr Stephens added one member of staff had been on long-term sick leave as a result of stress.

"Many of them are ex-police and ex-military personnel. To think that they can be reduced to going on the sick is totally unacceptable.

"They are out there to protect the public and people are vilifying them for that," he said.

To date there have been no criminal prosecutions as a result of the abuse.

Mr Stephens told PM the partnership's office staff were also forced to cope with high abuse levels.

"On a regular basis, almost daily, we receive items of objectionable material through the post," Mr Stephens said.

An Avon and Somerset police spokesman said: "We fully support the Camera Partnership and therefore we do not condone any abuse of its staff."