Out of curiosity, do you guys in Britain have your own form of crypo creature like bigfoot? Like, for North America, Mexico has the Chupicabra, the U.S. has the Sasquatch (or bigfoot), and Canada has the Yeti. Do you guys have your own version of anything like that?
Could be possible. People have been known to buy exotic animals like tigers and things like that, not realizing that they aren't going to be little cuddly cubs forever. Then, because they can't tell anyone that they have an illegal pet, they release them into the wild. It's why the Everglades down in Florida are overrun with Boa Constrictors. Just a thought.
Plus, things like Kangaroos are known to show up in random places (there was just one in Oklahoma), so the idea of a big cat getting somewhere doesn't seem too far fetched. At least not to me. Unless they're saying there's a 'hidden' group of big cats in South England. That's a bit out there.