Is Duncan starting to molt? Most of my English are blowing their coats right now (we aren't too far north from you) and will be plucked or sheared if they have not already been. If Duncan is in the same situation, he may have been ingesting the loose wool during normal grooming. So, it is a plus that you want to shave him anyway before it gets too warm because that will get all that extra angora off of him in the meantime.
That is good that you are giving him banana with the skin still on already, too. As far as papaya, I always skin it and slice it into small pieces (after de-seeding) before offering it. The skin is bitter tasting and you don't want to discourage him from eating it if he happens to take a bite of the skin before the fruit.
Is he still eating all of his hay? If so, I wonder if he is filling up on free-choice timothy + sprouted alfalfa and banana w/skin a few times a week, marigold, grape, arugula, kale, broccoli, black oil sunflower seeds, etc. That would be a much easier fix then if he has wool block, but if he is having wool issues then it is strange that his droppings are normal.
Best of luck!
Lauren