Better tell that to the RSPCA and the other clowns that release town foxes into the countryside, and I know that this definitely happens, as I have shot a number of the confused creatures.There is no license.
The license referred to in the previous link relates to the release of native species whose release is normally prohibited. For the list of those species you need to look at Schedule 9, parts 1, 1A and 1B of the Wildlife and Countryside Act 1981.
However the fox isn’t on that list.
The Animal Welfare Act 2006 places the onus on the person doing the releasing to ensure the animal being released in the wild will survive. This is why captured foxes are normally subjected to a “soft-release”, where they can be monitored and, if necessary, fed and looked after before being fully released into the wild. A “hard-release”, where the animal is simply dumped, is in breach of the Act.
I wonder which organisations go after hunts that don't follow the rules, erm, could one of them be the RSPCA???