Sift flour, salt and spice into a bowl. Rub in butter, add sugar, currants and lemon rind. Beat egg and milk, add to make a pliable dough. Roll out just under a quarter inch (5mm) thick. Cut out biscuits using a 3inch(75cm) fluted cutter and transfer to lightly greased baking sheets. Use scraps to make more biscuits. Bake at 375F, Gas Mark 5, 190C for 10-12 minutes. Cool on a wire rack.