The wildlife crime officers of the police have a liability to pursue the criminals in the case. I do not see that they have a liability to pursue the animals which remain the property of the farmer (indeed if he does not make efforts to recover them, he may be held responsible for any damage or injury they commit.) The boars, however, are native animals at large and are not themselves a crime.
So far as Wild Boar at large in Wales are concerned, it is pretty much inevitable that the Forest of Dean population will expand into the Marches eventually, with no criminal implication: and it is not the job of the police to control populations of native animals.
Unfortunately the police across the country have a tendency (a) to be as risk averse as the fools who are currently ruining the airshow business by disproportionate kneejerk reactions and (b) to seek power where they have no jurisdiction. A recent example picked up by the media was a cow seen grazing by the roadside in Northumberland, which was shot by a police marksman on the grounds that it wasn't in a field. Quite apart from the fact that it could have been herded into a field rather than dispatched, one really wonders how much the Northumberland police would panic faced with the New Forest, Dartmoor, Exmoor, various upland areas of England, Wales and Scotland, or indeed islands where cattle roam freely unfenced, crossing roads and interacting with the public frequently and peacefully. No doubt the armoury would be emptied and mass slaughter would ensue.
A certain respect is due to our guardians in blue but not blind faith in their rectitude, which is all too often based on what they think they should be in charge of and not what they actually are responsible for.
John