Released into the wild?
All land in the UK including the foreshore is owned by someone therefore to release or leave animals or birds on any land without the permission of the owner would presumably be an either a criminal or a civil offence. So action may be able to be taken against the people or organisations who do this if it is possible to catch them. If nothing else poor publicity for them if they advocate breaking the law.
It would also be poor publicity, even if they have permission from a landowner to release animals/birds on their land, if, by doing so they are releasing animals into an environment which they are not habituated to and are unlikely to survive in. If by introducing additional predators they raise those populations above the natural carrying capacity of that land they will be increasing the stress levels in both the introduced and existing populations. If this induces either or both sectors of that population to prey on domestic animals/birds or it raises the predator population to such a level that it cannot survive naturally within the confines of that land and part of the population then relocates unto the land of others who possibly do not wish this to happen then it would show that those who release these animals are, at the least acting irresponsibly if not illegally.
From this it follows that if the 'wild'/ 'existing' predator population is preying on domestic animals/birds then that predator population is above the natural carrying capacity for that environment and it would be prudent to reduce that population to a level where predation on domestic livestock or animals is at a nil rate. It could be argued that those who unbalance populations of predators or raise them above the natural carrying capacity of the land have at least a moral duty if not a legal duty to compensate those who lose livestock or animals and also compensate them for the costs of controlling the predator population.
These are just my thoughts on the matter, I am not a lawyer and do not have a detailed knowledge of the law on these matters but to me it suggests that those who release or relocate predators know or care little about the management of the environment for both economic and recreational purposes and are influenced by sentimental and anthropomorphic views of the countryside.
As an example of general ignorance I was speaking to someone recently who was dismayed about the large reduction of ground nesting birds on her patch of land. I mentioned the increase in the badger numbers on her land which she thought was wonderful but they couldn't have anything to do with it as they were veterinarian. A small natural history lesson ensued followed by disappointment when I told her it was illegal to cull or disturb badgers in any manner.
Bob