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There are thought to be four or five people in the gang, which may also be behind similar robberies around the country.

Their method is for two people to draw staff well away from the targeted items. Then another gang member acts as lookout while a fourth unlocks the cabinets and removes the objects. They then relock the cabinets, and leave. The operation takes only minutes and the gang appear not to be put off by security cameras.

In the Banbury theft, two men and two women were involved. The police have issued a description of the man who removed the items from the cabinet as white and stocky, with dark thinning hair and wearing dark clothing. The other man was white, aged about 40 and bald. He was wearing jeans and a short jacket. The woman with him was white, in her twenties with shoulder-length dark hair. She was casually dressed.

The second woman near the cabinet was described as white, with long black hair and glasses.

Anyone with information is asked to contact PC Simon Woodman via the Police Enquiry Centre on 0845 8505505. Information may be left anonymously with Crimestoppers on 0800 555111.