But it is not Sir David Attenborough. For one thing, Attenborough's animals always appear on cue. The creature which Nigel Brierly, a retired biologist, is stalking may not even exist. The Beasts of Exmoor, Bodmin Moor and elsewhere, have lived and thrived in the tabloids for more than a decade but to date remain as elusive as the Loch Ness Monster. Farmers in the area regularly find the carcasses of sheep which appear to be the victims of "clean" cat kills rather than the indiscriminate savagery of dogs. Others claim to have come face to face with the Beasts, though cynics might add that most of these incidents seem to occur after closing time.
Despite its title, Encounters: the Call of the Beast does not present us with a single puma, lynx, panther or bobcat, or even so much as a large domestic tabby, but the assortment of characters on its trail is so odd that you never really notice. As well as Brierly, the acknowledged expert on the phenomenon ("I've been looking a bit longer and am a bit madder than the rest"), and his loyal sidekick, Jacky Cullingford, we meet two London policemen who spend their weekends bringing their forensic and surveillance skills to the hunt. Graham Quick, a freelance photographer, is determined to take the first incontrovertible snap of the creature, and sets off in pursuit with an empty onion bag, two tins of cat food and a large supply of toilet paper for long nights in the wood. "The fact that I've been trying for so long makes it important to me," he says. "I'd be really pissed off if someone else went out and snapped it tomorrow. But I know that I've as much chance as winning the lottery."
Also out there somewhere is John Waters, who originally researched the programme and whose interest in the Beast is professional, not obsessional. Waters is a full-time wildlife photographer, well used to spending days or weeks in his hide before his quarry appears. Even he, however, eventually returns from the moor admitting defeat.
And defeat remains the only characteristic which unites these people, though it is something you feel they will happily endure if it means that no one else gets there first. If a disinterested hiker or birdwatcher were to stumble across a puma corpse one morning, life would suddenly cease to have meaning for most of the Beast fanatics. Yet the very fact that no one has ever found a dead puma suggests that Brierly and the rest are chasing a fantasy.
Brierly, author of They Stalk by Night, will not be deflected by those resisting conversion. He regularly sets traps and boils droppings, looking for a result in the cause of natural history. His dedication is such that recently he and his wife heard what they believed to be a puma howling outside their bedroom window. They rushed downstairs to try and mimic it on the piano.
Frances Berrigan, producer of the film, is no wiser as to the existence of the creature even after making the programme. "I suppose it's conceivable that there's something lurking there,'' she says. "I'm tempted to say that Bodmin and Exmoor are full of legends of highwaymen and pirates and things that go bump in the night. It's just the sort of place you'd expect to find a `monster'."
Together with director Norman Hull she was determined not to send up the cat hunters too much. "We wanted to put a bit of oomph into these people's amateur efforts," she explains. "It's nice to see a film amid all the blood, gore and misery on television that turns up a smile, yet doesn't debunk the whole thing."
That the documentary throws up no further evidence has not disappointed her. "What we really wanted to say was that the Beast of Exmoor in its romantic appeal can be compared with the Loch Ness Monster," Berrigan explains. "People like to think that there's something out there larger than themselves - it adds shape and colour to their lives. When we were down there almost everyone had a story. So whether or not it's true, it's still important because it's dominating so many people's lives."
Encounters (Sun 7pm C4)