Police are investigating an allegation that a fox was killed during a traditional hunt meet, in a breach of the ban on hunting with dogs.
The animal was chased and killed near Sturminster Newton, Dorset, by hounds from the Portman Hunt on Wednesday, the League Against Cruel Sports said.
The campaign group has called on the National Trust to revoke the Portman Hunt’s trail hunting licence.
The incident at Fifehead St Quintin was witnessed by hunt saboteurs, who recovered the “disembowelled” fox, the League said.
Chris Luffingham from the group described it as a “brutal incident in which a wild animal has lost its life”.
The league said the National Trust should revoke a licence granted to the hunt at the Kingston Lacy estate, 11 miles (18km) away.
The trust said it could not comment because the incident did not take place on its land.
Dorset Police said it was investigating an allegation of an “illegal hunt and that a fox was found dead”.
In a statement the hunt said it would fully cooperate with the police investigation.
A spokesperson said: “The Portman Hunt operates within the law to comply with the Hunting Act 2004.
“Despite this, the hunt – along with many others across the country – is regularly subjected to spurious allegations of illegal hunting as part of a wider animal rights agenda.”
Under the Hunting Act, it is illegal to hunt a wild mammal with a dog, except in specific circumstances.
Many hunts say they only engage in trail hunting, in which hounds follow an animal scent trail left by hunt members on foot, horseback or from a quad bike.
The Countryside Alliance says that if hounds pick up the scent of a real fox the huntsmen will stop the hounds as soon as they are made aware.
In March, the Portman’s joint-master Evo Shirley was found not guilty of illegal hunting after police received footage of hounds chasing a fox.