So maybe we need tighter legislation for rabbits too? And rats?
I don't think so. There is already animal welfare legislation in place that gives all animals protection against cruelty, and any shooter who violates that legislation can be prosecuted, whether it's boar or rats.
Adding additional raft of legislation to boar would just turn it into another elitist branch of shooting sports.
I look at this from the point of view of a landowner. If feral boar were to turn up on my land, it should be up to me whether or not they get shot (or trapped), when, and by who, depending on the level of crop / habitat damage that I would be prepared to tolerate in return for having a new addition to our native fauna (which, Incidentally, I welcome), and whether I was interested in cashing in on the sporting element, or maybe just enjoy shooting a few myself. I don't need any additional legislation over and above what already exists to help me make those decisions. And neither would I want someone coming along claiming that they were one of the few people who are "qualified" to shoot boar, and that I'd better hand the management over to them...
Anyone who's grown up and sensible enough to be trusted with a firearm in our crowded country out to be capable of self regulation.