A former Natural History Museum worker who thinks he has captured the Westcountry's Loch Ness Monster on film claims what he saw could be a dinosaur thought to have died out 65 million years ago.

John Holmes, 49, has released footage of the legendary Cornish beast Morgawr, which he filmed three years ago in Gerrans Bay, off the Roseland Peninsula.

He believes that the creature could be a plesiosaur - a long-necked, marine reptile with four paddle-like limbs, thought to have become extinct with the dinosaurs.

Mr Holmes, of Sticker near St Austell, said: "My pet theory is that it was a living fossil. I think that there is a group of plesiosaurs going around in the oceans of the world.

"All around Britain there have been sightings of sea serpents."

He said the footage showed the head of a 2.2-metre long creature, rising about one metre above the water.

Mr Holmes, who worked as a higher scientific officer at the Natural History Museum for 19 years, said that he had waited so long to release the film for fear of being ridiculed. But, after showing it to experts during the last year, they all seemed puzzled as to the creature's identity.

"What caught my attention was the bizarre movement out to sea," he said. "The hairs on the back of my neck stood up. It wasn't gargantuan, but big enough to rule out marine birds."

A decayed carcass netted by a Japanese trawler near New Zealand in 1977 has often been claimed to be a likely plesiosaur, but it later turned out to be a decayed basking shark.

Meanwhile, sightings and images of Morgawr have been reported since the early 1970s, and some say for more than 100 years. In May, the cox of the St Piran patrol boat and a fisherman, both from Falmouth, claimed to have spotted the creature in separate incidents on the same day.