Preheat oven to 180 degrees C. Grease two 23cm round cake tins.
Sift together flour, baking powder, soda, salt, cinnamon, allspice and ginger.
Mix together buttermilk, potatoes and raisins in a medium bowl.
In a large bowl, cream butter or margarine. Gradually add white and brown sugars, creaming until fluffy. Add eggs one at a time, beating thoroughly after each addition. Beating only until smooth after each addition, alternately add dry ingredients in fourths and potato mixture in thirds to creamed mixture. Turn batter into prepared pans and spread evenly.
Bake for about 30 minutes, or until cake tests done. Cool and remove from pans. Frost as desired.