Members of the public have reported sightings of of a black panther in fields near Gatwick airport.
Joanne Walsh, who works for Southern Rail, said she was travelling on the train from Brighton to Croydon when she noticed the big cat.
She said the animal was about half the size of a cow.
She added: "It was a large black animal moving in a cat-like manner with very defined muscle tone and a long tail.
"My perception was that it was stalking cows in the adjacent field. Although it was approximately 100ft from the cows the animal appeared to be almost half the size of one."
Earlier this week, Mark Fraser, of Big Cats In Britain, said he believed panthers were living in the UK countryside.
Mr Fraser said he had received numerous sightings of big cats from Cornwall, near the Eden Project.
It was no longer a question of whether big cat cats existed in Britain, he added, but what different species were out there.
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