Preheat oven to 325 degrees F. Place bacon into a dry pan. Heat to render fat and fry bacon. Add onion and kidney. Season with cayenne, salt, and black pepper. Saute another 2 minutes. Transfer to a bowl and add bread crumbs, rosemary, and egg.
Place stuffing in lamb, packing tightly. Tie up like a parcel. Tuck the edges of the meat underneath the string. Dust the outside of the meat with flour. Season with salt and pepper and brush with butter. Place on a rack in a baking dish. Cook for 1 hour, 10 minutes.
Mix together honey, mustard, Worcestershire sauce. At 1 hour, 10 minutes, baste the meat with the honey mixture. Add 1/2 cup of the cider to the roasting pan to prevent honey mixture from burning. Cook 1/2 hour more, basting from time to time.
Remove the meat, cut off string, and place meat on warmed serving dish. Pour excess fat from baking pan. Deglaze pan with 1/2 cup cider, bring to boil. Strain.