Combine sour cream, horseradish cream, mustard, Worcestershire sauce, vinegar, hot sauce, salt and pepper in a bowl. Cover and refrigerate for at least 1 hour before required, longer if time permits. Stir chives and dill into sauce just before serving.
Preheat oven to 200°C. Remove beef from refrigerator 30 minutes before cooking to allow to come to room temperature. Rub with oil and season well on all sides.
Heat a roasting pan over medium- high heat. When hot, add beef and cook for 10 minutes, turning until browned on all sides. Transfer pan to oven and roast for 25 minutes for medium rare. Transfer to a platter and cover to keep warm. Stand for 10 minutes before slicing and serving with horseradish sauce.