Place mashed potato in a bowl; stir in tuna fish, canned sweet corn and chopped parsley. Season to taste with salt and black pepper, then shape into eight patties.

Press the fish cake into 50g/2 oz fresh breadcrumbs to coat them lightly, then place on a baking sheet. Cook under a moderate grill until crisp and golden, turning once. Serve hot with lemon wedges and fresh vegetables.