London - The criminal underworld has taken out a death contract on a highly skilled sniffer dog operating in Manchester Prison in northern England, the Guardian newspaper reported on Tuesday.

The prison service has refused to name the dog, but a spokeswoman acknowledged there had been "tangible death threats against the dog because it is so successful".

"He was 100 per cent more sensitive than some drug dogs and he was also 100 percent more accurate," the spokesperson said, adding the dog was key to helping reduce drug supplies through social visits.

The prison, formerly known as Strangeways, has three labradors, two spaniels and a collie. They are used to search visitors standing in line to visit inmates, and the dog's success rate was soon noticed. - Sapa-dpa