Beat the cooked potato to a smooth purée with the milk and egg. This is best done in a liquidiser.
Mix all the dry ingredients for the scones together with the fat.
Fold the flour mixture into the purée. Do not overmix and do not leave to stand at this point or you will lose the light structure to the scones.
Spoon the mixture onto a greased baking tray or use greased individual pattie tins or a bun tray. Bake in a preheated oven, gas mark 7, 425°F, 220°C, for 15 - 20 minutes until brown.