Combine first 5 ingredients in a small bowl; cut in margarine with a pastry blender until mixture resembles coarse meal. Stir in currants. Add 2 tablespoons plus 1 teaspoon milk, stirring with a fork just until dry ingredients are moistened.
Sprinkle 1/2 teaspoon flour evenly over work surface. Turn dough out onto floured surface, and knead 4 or 5 times. Roll dough to 1/2-inch thickness; cut into rounds with a 2 1/2-inch biscuit cutter. Place rounds on a baking sheet coated with cooking spray. Bake at 425° for 10 minutes.
Combine powdered sugar and 1/2 teaspoon milk, stirring well. Drizzle glaze over warm biscuits.