Mix together the sultanas, sugar, treacle, bran, mixed spice and milk in a bowl. Leave to stand for 20 minutes to allow the bran to soften. Stir in the flour.
Tip the mixture into a greased and lined 1 kg (2 lb) or 1.3 litre (2¼ pint) loaf tin (see page 15) and level the surface. Bake in a preheated oven, 160°C (325°F), Gas Mark 3, for about 45 minutes or until risen, firm to the touch and a skewer inserted into the centre comes out clean. Loosen the cake at the ends and transfer to a wire rack. Peel off the lining paper and leave to cool. Cut into slices and spread with a little butter to serve.