During an overnight raid a pen holding the birds was broken into, and 230 of the birds were killed in what has been described as a “callous and sustained” attack, before being removed.

A few pheasants managed to escape, but were found dead under nearby bushes. Police have said that the injuries sustained indicated that they had been beaten to death.

Lothian and Borders Police have suggested that the birds were stolen with the intention of offering them for sale, but warned that the birds are not fit for human consumption, as they were being treated with veterinary drugs for a respiratory disease. It is not thought that the pheasants would be highly toxic if ingested, but one of the birds found at the scene has been sent for analysis in order to determine the risk.

Pc Jim McGovern, wildlife crime officer with Lothian and Borders Police, said: “It is highly likely that these birds were bludgeoned to death. My biggest concern is that someone will try to reintroduce them back into the food chain.

“These birds are going to be very heavily bruised. I would urge anyone, particularly those in the pub and restaurant trade, who may be offered a large number of pheasants to contact us.”

Anyone with any information should contact Lothian and Borders Police on 0131 311 3131, or Crimestoppers in confidence and complete anonymity on 0800 555 111.