Experts can't agree on whether or not Great White sharks have been spotted swimming off the coast of Cornwall.
Several fishermen and holidaymakers claim to have seen the fearsome fish lurking in the waters there, not far from the coast.
But shark scientist Douglas Herdson said he thought it was unlikely because the big beasts are very rare.
Other experts disagreed and said so many reported sightings meant it very likely Great Whites are in UK waters.
Shark conservationist Richard Peirce said: "I am almost certain that Great White Sharks appear off the coast."
But Mr Herdson disagreed. He said: "Temperature and conditions here are all fine, and I'm sure they have been here in the last 3-4,000 years, but they are now so rare it is very unlikely."
Lobster fisherman Brian Bate, from Padstow in Cornwall, thinks he definitely saw a Great White on a fishing trip a few years ago.
He said: "I saw this big thing breach out of the water.
"He looked like he was tail towards me. I could see his back and as he came up he twisted sideways.
"I thought, 'What was that?'. It was quite a size to come leaping out of the water."
Even if Great Whites are visiting UK waters they are so rare that they are no threat to people.
You can find out more about shark sightings by watching Sharks: Great Whites in Great Britain on BBC One on Sunday at 7pm.