1) Preheat the oven to 220C/Gas 8.
2) In a large bowl, whisk together the flours, baking powder, bicarbonate of soda, sugar and salt. Cut in the butter until the mixture resembles coarse meal. Add the buttermilk to the dry ingredients, stirring until the dry ingredients are moistened.
3) Turn the dough out onto a lightly floured surface and knead lightly four to five times. Roll or pat the dough out to about 2 1/2-cm thickness. Cut with a biscuit cutter and place on an ungreased baking tray. Bake for about 12 to 14 minutes or until brown.