Preheat oven to 350-degrees.
Coat an 11-by-7-inch baking dish with cooking spray.
Bring 4 quarts water to a boil in a large Dutch oven. Add rutabaga; return to a boil, and cook for 3 minutes.
Add potatoes; return to a boil, and cook 1 minute. Drain well, and return to pan; set aside.
Place flour, salt, and pepper in a medium saucepan. Gradually add milk, stirring with a whisk until blended. Bring to a boil over medium-high heat, and cook 1 minute, stirring constantly.
Remove from heat and add the cream cheese and Worcestershire sauce, stirring until the cheese melts. Pour over potatoes and rutabaga; toss gently to coat.
Spoon mixture into prepared baking dish. Cover with foil and bake for 45 minutes.
Sprinkle breadcrumbs and parsley over casserole, and bake, uncovered, an additional 15 minutes.