It's a complicated issue. Animal welfare in this country depends very much on the care (or lack of) from the owner and relying on the human's sense of responsibility to the animal. As the ads demonstrate, it is all too commonplace for some people to swap/sell/give away animals without a second thought.
I have heard a suggestion that a licencing scheme should be brought back for dogs, modelled on vehicle registration with 'logbooks', to introduce more responsibility - but for that to work, you'd be talking about funding something the size of DVLA to register animals - can you see that happening?
The reason I was looking in the first place was because someone brought this to my attention:
www.gumtree.com/p/pets/american-bulldog-puppies/79005339
I despair of backyard breeders. AmBulls are going the way of the Staffie unfortunately. Uninformed people breeding from semi mature dogs in this case is not the way to go with a large breed that has associated health issues like hip dysplasia and NCL and if not socialised and trained properly, could be potentially dangerous.