I recall, perhaps a couple of years ago, another member from Trent's neck of the woods who took pride in feeding feral foxes. The fact that he was encouraging foxes to live in an environment which was less than suited to their normal lifestyle was of little consequence to him. I recall doing a little investigation into the effects of semi-urban living on foxes and learning that - because they were living in (for foxes) a crowded environment their health suffered. In particular, it appeared that mange was endemic and that this resulted in a high death rate among cubs.
As has already been stated, a fit and healthy cat is quite capable of dealing with a fox. I even recall seeing a fox running away from my own cat, who, though small, was puffed up like a football and bouncing up and down on her toenails. (She didn't like dogs and I had to warn dog owners who came to visit.)
I suspect that - to some extent - some of the Croydon cats may be victims of foxes but also that the police are using this as a means of getting out of an investigation they are not comfortable with ...