In a large bowl combine cream cheese, 4 ounces of shredded cheddar cheese, mayonnaise, sour cream, Old Bay, worcestershire sauce, lemon juice, and ground mustard. Stir together until well combined.
Add the lump crab meat and gently fold it into the mixture doing your best to break apart the meat as little as possible.
Spread the mixture into a lightly greased 1.5 quart baking dish and top with the remaining shredded cheddar cheese and a sprinkle of Old Bay seasoning.
Bake for 25 - 30 minutes or until the dip is hot and bubbling.
Serve with your favorite crackers, bread, chips, or veggies.