Make a pocket in the loin by cutting, with a sharp knife, to within 1/2 in. of both ends; sprinkle with salt and pepper.
Pit prunes; peel and dice apple, sprinkle with lemon juice.
Stuff pocket with prunes and apple.
Roll meat firmly around filling, secure with string.
Rub scored crackling around loin lightly with salt.
Melt butter in baking dish; add pork.
Cook in moderate oven, Mark 4, 350°F., approximately 11/2 to 2 hours.
Make thin gravy from pan juices.
Red cabbage makes a good accompaniment.