i will completly agree with this and i wish the govenment would take a look at new zealand or similer places where to own an animal you have to for go numerous checks including a house check, job, mental ability to train etc and then if you pass you pay a yearly cost to keep your animal or more if your a breeder.
i do also agree with Lovejoy and Tinker as to weather the dog should be put down, i dont condone dogs biting people and untrained dogs being off their leads. By the looks of things the dog more than likely was thinking it was guarding its land, i only say this as the op said there was a caravan on site and the dog being loose, now thats the owners fault for not properly sectioning off the property not the dogs.
anyway hope the op is ok and not to badly shook up from the ordeal and doesnt look at all dogs in this light, i would also go and take some photos of the area if the sites not properly sectioned off as thats also health and saftey factor to you the public from the site owner