Avon and Somerset Police have been advising local shops and offices to keep their CCTV systems in top condition during the Christmas period.

Close-circuit cameras play a vital role in identifying criminals but the images can often be of poor quality if the systems are not properly maintained.

Police have been advising companies to carry out a number of activities including keeping the lenses clean, changing the tapes regularly and monitoring the pictures to ensure they are in focus.

Crimestoppers presenter Insp Keith Jones said: "We have an 80 per cent success rate in identifying offenders where there is a good-quality video or clear pictures of the culprits which can be used on television and in newspapers.

"But unfortunately we have had a number of serious incidents where videos which could have helped catch criminals could not be used because of the poor quality of the tape, or staff had forgotten to turn on the recorder."

Images can often become blurred if the same video tape has been used continuously for months or if the camera lens is dirty.

Insp Jones explained the importance of keeping the systems in good condition.

He said: "A video is only as good as the quality of the equipment and tape. We would urge firms to spend a few pounds extra, to ensure they work effectively."

Avon and Somerset police have also launched a new campaign which aims to crack down on the number of thefts from cars by reminding shoppers not to leave their property in parked vehicles.

During the next few weeks, posters will be displayed around car parks carrying the message "If you leave it on view, the next victim's you!"