The Beast of Bodmin, if it exists, is a large wild cat (or perhaps a number of them) like a Puma, which has been sighted on Bodmin Moor over recent years. It appears that there were occasional reports from farmers of mutilated bodies of sheep being found on the moor. These reports seem to have evolved into the belief that a large wild cat was carrying out the killings. People started "seeing" the beast as well.
Eventually the Ministry of Agriculture, Fisheries and Food conducted an official investigation in 1995. This study could find "no verifiable evidence" of foreign large cats, and concluded that that the mauled sheep could have been attacked by animals common in Briitain. However this government report also said that "the investigation could not prove that a 'big cat' is not present."
Sightings of the Beast of Bodmin Moor still continue. In October 1997, officials from Newquay Zoo claimed to identify pawprints left in mud to the south of Bodmin Moor as the tracks of a puma. In August 1998 a 20-second video was released and some wild cat enthusiasts believed that it definitively showed that big cats roam Bodmin Moor.The Natural History Museum, Beast of Bodmin Moor page records how the museum determined that a skull found in the area in 1995 was of a leopard. It belongs to a leopard (Panthera pardus to give it its scientific name. Leopards are found in Africa, the Middle East and southern Asia), but the it came from an animal that died outside Britain, and was probably part of a leopard skin rug.
The RAF tried to find it with night vision glasses in 1999, but failed.
A detailed write up of the government moves to investigate big cats is to be found here.
The BBC report on the situation in March 2006