Boil the potatoes in lightly salted water until tender, drain and keep warm. Meanwhile, sprinkle the cod with the curry powder and rub all over the fish. Heat the oil in a large frying pan and cook the cod fillets for 4-5 minutes on each side until cooked through. While the fish is cooking, poach the eggs in a pan of boiling water and keep warm. Mash the potatoes with the chives, then mash in the prunes and natural yoghurt. Serve the fish on a bed of mash, topped with a poached egg.