Preheat oven to 220c.
Whisk the flour, sugar, baking powder and salt together in a large bowl.
Using two knives or a pastry cutter, cut the margarine into the flour until sandy.
Stir in the raisins or sultanas.
Mix in the milk, yogurt and vanilla and stir until just combined.
Using your hands, gently form the mixture into a ball and place on your baking tray.
Flatten until you have an inch thick disk. Brush with milk and sprinkle with sugar.
Cut into wedges and gently separate. Bake for 12-15 minutes until golden.
Leave to cool before breaking apart to eat!