Peel potatoes. Cut into 1 inch cubes. Cook in boiling salted water to cover, 12 minutes or until tender. Do not overcook. Drain and cool.
Stir together mayonnaise, sour cream, horseradish, parsley, salt and pepper.
Add cubed potatoes, egg, bacon and green onions. Toss gently. Cover and chill. Serves 6.