A British farmer who hanged his sheepdog from a tree has been sentenced to 18 weeks' jail, local media reported.

Graham Thomas, 55, was handed the sentence at a hearing at Newport Magistrates' Court on Wednesday (March 21), the Caerphilly Observer reported.

Thomas had strung his sheepdog Prince with a rope from a tree, after it purportedly failed to round up sheep.

Thomas, who is from Rhymney town in the county borough of Caerphilly in south-east Wales, Britain, told the court that the dog's death was "accidental".

He claimed that Prince ran up the tree with the rope, which became twisted around it, The Sun reported.

However, a vet said such a situation was highly unlikely.

Three witnesses contacted the Royal Society for the Prevention of Cruelty to Animals (RSPCA) with information on what happened to the Welsh border collie.

They said they had seen Thomas shouting and swearing at Prince before the hanging.

Thomas was banned from keeping dogs or sheep for life, The Times reported.

The Caerphilly Observer quoted RSPCA inspector Emma Smith, who said: "This is such an unusual and disturbing case where a sheepdog was killed by his owner allegedly because he wouldn't round up his sheep properly.

"Prince would have suffered immensely which resulted sadly in his death. This deliberate cruelty is just so horrific to fathom. Following the incident his body was then removed by the defendant and burned."

Under Britain's Animal Welfare Act, anyone who is cruel to an animal or does not provide for its welfare needs may be banned from owning animals, fined up to £20,000 (S$37,000) and/or jailed.