Preheat oven to 350º F.Cook the macaroni as directed on the package.
While the macaroni is cooking, melt the margarine in a 3-quart saucepan over low heat.
Stir in the flour, Worcestershire sauce, mustard, salt and pepper.
Cook over medium-low heat, stirring constantly, until the mixture is smooth and bubbly.
Remove from the heat and gradually stir in the milk. Heat to a boil, stirring constantly. Boil and stir for about 1 minute.
Stir in the cheese. Cook, stirring occasionally, until the cheese is melted.Drain the macaroni and gently stir into the cheese sauce.
Pour into an ungreased 2-quart casserole and bake in the oven, uncovered, until bubbly (for about 20-25 minutes).