Drug barons have made death threats against a prison dog, because it is doing its job too well.
The dog cannot be identified for its own safety
Tests found the animal from HMP Manchester - whose identity is kept secret for protection - was 100% accurate in sniffing out drugs.
The sharp-nosed canine is said to have played a key role in reducing the amount of drugs in the jail.
A Prison Service spokeswoman said: "Tangible threats had been made to kill the dog because he is so successful."
She added: "Drugs in prison are such big business that people are prepared to make threats against a poor, defenceless dog."
Yet in her latest report on the prison, formerly known as Strangeways, Chief Inspector of Prisons Anne Owers raised concerns that the dog was "not operating in line with others at the prison."
Prison chiefs responded by testing the dog, which is trained to sit down next to someone believed to be carrying even traces of illegal drugs.
"He was perceived to be indicating a far higher rate than the other dogs and was taken out of commission for a few days to be re-tested," said the spokeswoman.
She added: "He was found to be 100% accurate on every test."
Prison officers use six dogs to check visitors for drugs - one collie, two spaniels and three labradors.
The number of inmates who tested positive in compulsory drug tests was 30% in 2003-4 but this has dropped to 13% since April - a fall attributed to the dog's success.
Visitors suspected of smuggling drugs are turned away if they refuse a search or are offered a closed visit - behind a glass screen - at weekends.