Strangely enough being the person who saw it I’m not 100% convinced. I’d only be that if I’d seen the whole animal. Covering up the head / shoulder of the animal in colournoise’s picture gives a fair approximation of what I saw. Although I was looking broadside.
There was a big change in the law in the mid 1970’s where the requirements for keeping big cats became more onerous. You could buy them at Harrods! It wouldn’t be improbable that some got dumped but that was over 25 years ago.
I could see big cats avoiding detection. Foxes going to be more common but you don’t see too many of them when just out for a ride, same goes for badgers and otters.