Mike Freebury, a member of the Animal Pathology Field Unit, has investigated the mystery of 'cattle mutilations' for a number of years.
The phenomenon, first reported in America in the 1970s, involves the unexplained deaths of rural animals.
The bodies are often discovered with missing limbs and organs, removed with surgical precision.
Mike says that the illegal attacks are also happening in Britain - and UFOs are responsible.
"Certainly, in my opinion, the UFOs are something that relates directly to the animal mutilations," he told BBC WM presenter Brett Birks.
"They're often seen around the areas where mutilations are taking place. I think that the animal mutilations are possibly some sort of sampling programme being carried out by the entities that are propelling these crafts."
"We have carried out a number of surveillances on Dartmoor," he said.
"We were never able to catch the perpetrators in the act but we have seen some very strange craft of unknown origin. UFOs. We have them on film. We've managed to get frame-by-frame analysis of them done. It appears that these things were appearing literally within a second and then gone."
In rural Britain, dead sheep are being found by famers with mysterious - and gruesome - injuries. Mike says a "highly active" area in the UK includes Shrewsbury, Dartmouth and parts of Wales.
"We're talking about some fairly remote areas," he said
"These injuries to the animals - the animals are invariably killed - are very specific. If you've seen some of the bodies that I've seen, it's just absolutely incredible.
"The flesh appears to have been cauterized indicating some sort of thermic lance or micro-sonic wand has been used. We're talking incredible technology. There is never any blood."
Mike says they're have been 40,000 estimated cases in America since the 1970s. The number in the UK remains unknown.
"You do have to question - how is it that somebody has not been identified?" he said.
"(How is it that) somebody has not been arrested or charged with these crimes? There's never been a single prosecution. And it's the same in this country.
"It's plainly evident that these (attacks) are not carried out by natural predators."
The APFU are currently conducting a survey called Project Corridor, an attempt to quantify the number of attacks in Shropshire. Mike explained:
"(The attacks) are a crime. They're a crime under the Criminal Damage Act. I would say to you that the farmers themselves seem to accept that not only is there a problem but in many cases they are describing what appear to be craft of unknown origin flying over their land and they are pointing the finger at them for carrying out these attacks."