Stories of these big cats have been circulating for so many years now that if true then they are either breeding or a fresh stock is being occasionally released. There has been so many different species reported which would also mean there must be a considerable number out there as it is unlikely they are interbreeding. I think it pretty likely that some have been released or escaped but I think these would have been seen very quickly on the first few days as the animals would be disorientated at first and if released from captivity would probably not have their more normal wild instincts tuned in, in which case I would have thought they would be quite vulnerable for some time after being released. If they have been breeding I would have thought that a vulnerable time too as they would have to remain in one area for a short time. Regards actual proof that is a bit of a grey area, one would think in our crowded land there would be more positive proof, when out in the countryside it is easy to feel you are remote and the only one for miles but there is an incredible variety of outdoor activists out there all doing their thing and youd have thought the proof would be more definite considering the number of reported sightings. That being said we know for certain otters are in our rivers but the majority of people have never seen one and there are some people that have never seen a badger which are incredibly common, in a local wood I know of people who live close by have never seen the deer there. The difference is if you wanted to prove the otters/badgers/deer were there with a bit of care dedication and time you could do so whereas the cats remain elusive, it seems to me maybe wrongly that more people have apparently seen a big cat than an otter. For me the jury is still out and I remain open-minded, I do feel however that some folks lose all rationality with the unexplained, I once proved a ghost to be nothing more than an owl.