1. Preheat the oven to 425°F/220°C/ Gas 7. Grease a baking sheet.
2. Sift the dry ingredients into a bowl. Rub in the butter or margarine with your fingertips until the mixture resembles breadcrumbs.
3. Gradually pour in the buttermilk, stirring with a fork to form a soft dough.
4. Roll out the dough until about 1/2 in (1 cm) thick. Stamp out rounds with a 2-inch (5 cm) biscuit cutter.
5. Place on the prepared baking sheet and bake until golden, 12-15 minutes. Serve warm or at room temperature.