Other scientists, however, do not believe the animal could propelled itself so far into cold waters.

A source with knowledge of the illegal trade in exotic animals said it was more likely that the shark had been caught alive in order to be sold, possibly into a private collection, and then dumped overboard.

“It is incredibly unlikely that the shark could have made it this far under its own steam,” he said.

“The risk is that it was caught and illegally transported to be an exhibit.”

With their spindle-shaped bodies, short head, bulbous pointed snout and large eyes, crocodile sharks tend to grow to a maximum of three and a half feet and usually weigh less than a stone.

Not considered dangerous to humans, the species takes its formal name, Pseudocarcharias kamoharai, from the Japanese expression for “water crocodile”.

Steven Greenfields said he and his family were “stunned” when they spotted the shark during a walk on the beach and contacted their local aquarium.

“I have experience with sharks whilst swimming and diving overseas, but, despite a fair amount of fishing and swimming in the UK all my life, have never seen any shark in UK waters other than dogfish,” he said.