Your poor bull terrier is not able to talk to you and let you know why he is itchy and has to scratch all the time. There is no way for him to let you know what it is that he has wrong with him that is making him do this nonstop scratching. So as a dog owner it is your duty to try and figure out why he is doing this so that you can help him with his discomfort.
OK, first off, not matter what all dog breeds are going to itch occasionally for one reason or another, so do we, dry skin, bug bite, you name it, it happens and it's temporary. However is your dog doing it so much that he is losing his hair and even getting to the point of bleeding? If so, then it's time that you do something about it.
You should first try to figure out what might be causing this. Is it the diet you are giving him, the doggie treats, the human food you've been sneaking him at the table? Try and stop doing the treats and table food and see what happens. Try changing his diet to a more natural formula and see what happens.
If the food issue doesn't improve your dogs scratching habits then you should take him into to see the vet. There are times that the dog simply has some sort of skin irritation and your vet can give him a shot of steroids and this generally will do the trick in a few weeks. However, if that doesn't work the vet might want to send a skin sample to a doggie dermatologist so they can check further into what might be causing the itching.
Of course if it happens to be the beginning of fleas you can always make sure to get the special flea treatment that your vet will recommend and then make sure that you also bathe him often with a parasite control shampoo that you can also get from your vet. This should be done once a week until the scratching goes away.
Your dog also might be scratching because they are bored or lonely and are in need of attention and you can fix that problem by giving him plenty of attention and taking him outside often to play and to go for walks. Make sure that he has plenty of different toys to keep him distracted from wanting to itch and that will be fun for him to play with.
You dog also may have an obsessive compulsive disorder, and yes dogs can develop disorders like these just like humans. If your vet things this is the problem he will more than likely prescribe a medication to help control this kind of compulsive behavior.
Note: If you dog has to go on steroid therapy you should know that this therapy is going to make him very thirsty and he will have to relieve himself more often, so make sure that you keep an eye on his water dish and when he needs to be let outside.