@ ceetee : The RSPCA's website refers readers to an external link 'The Fox Website' whose line is that it is relatively rare for a fox to attack a fully grown cat (as opposed to a kitten).

''In an area of north-west Bristol with 1,225 pet cats, 8 (0.7%) were killed by foxes in a year and these were mainly kittens. This is an area with a high density of foxes and pet cats: one average fox home range included about 100 pet cat ranges, this is about 1 fox per 100 cats. Foxes can kill cats but this is rare and it is more likely that a cat will be run over by a car than killed by fox. This is not surprising as both species are predators armed with teeth and claws and are of similar size. Moreover, in Bristol fox densities were high; at lower, more common densities, it is likely that fewer pets will be lost.'' from The Fox Website