I'm sorry, I thought this was a hunting forum, not Mumsnet.
Big cats? All conjecture, posts and posts of what if's with very little evidence to back it up.
The UK could potentially host thousands of non-native species, but it doesn't mean they are here.
If you are convinced you have seen one, then it doesn't matter what anyone else thinks, but, chances are, you were mistaken and perhaps you are not the countryman you thought you were.
As for evidence, where are the road kills? RTA's are the biggest cause of death for big cats across the globe in heavy industrialised regio