In a medium saucepan melt margarine or butter. Stir in flour and salt. Add the milk all at once. Cook and stir until thickened and bubbly. Cook and stir 1 minute more. Stir about half of the hot mixture into the beaten egg yolks. Return all to saucepan. Cook and stir until mixture is thickened and bubbly. Stir in lobster, dry sherry, white or black pepper, and ground red pepper. Heat through. Serve over English muffin halves. If desired, garnish with snipped chives. Makes 4 servings.