It's gradually becoming more common
David Tomlinson adds:
Thirty years ago, Britain was free of lungworm (also known as hookworm), but this nasty parasite is now firmly established here. The blood-sucking lungworm looks like a roundworm, but it has teeth that it uses to attach or hook itself to the dog’s intestine. It changes the attachment site several times a day, leading to blood loss and causing anaemia and iron deficiency. Slugs and snails are the carriers, infecting foxes or dogs that eat them.
This is one worm that isn’t a threat to humans, but it can be deadly to dogs, though most make a full recovery if given the correct medication. If your dog doesn’t show any interest in eating slugs or snails you don’t have to worry too much.