Heat the oil in a flameproof casserole dish and add the pork. Cook over high heat for 10 minutes or until browned, stirring frequently. Use a slotted spoon to transfer the meat to a plate.
Reduce the heat to medium then add the carrots, celery, leeks, bay leaves and sage. Cook for 5 minutes, stirring often, until the leeks are softened. Pour in the cider and stock. Return the pork to the casserole with any juices. Add the mustard and mix well.
Bring to the boil then reduce the heat to low and cover. Simmer gently for 45 minutes. Stir in the potatoes and swede. Bring back to simmering point, cover again and cook over low heat for 30 minutes or until the pork and vegetables are cooked.
Meanwhile, for the dumplings, mix the breadcrumbs, flour, baking powder, chives and parsley in a bowl. Make a well in the centre and add the egg, milk and oil. Mix the liquids together then gradually stir in the dry ingredients to make a dough.
Bring a pan of water to the boil. Dust your hands with flour then divide the dumpling mixture into 12 portions and roll each one into a round dumpling. Add the dumplings to the water, adjust the heat so that they simmer gently and cook for about 10 minutes or until risen and firm.
Use a slotted spoon to lift the dumplings out of the water, shaking gently to drain them well, then arrange them on top of the casserole. Serve at once.