Preheat the oven to 180 degree centigrade/160centigrade Fan/Gas Mark 4.
Put the weetabix and sultanas in a bowl. Pour the milk and water over the top and leave to soak up all the liquid.
Stir in the flour, mixed spice, sweetener and beaten egg.
Spoon the mixture into a 450g lined loaf tin and baked in the preheated oven for 1 1/4 hours, until cooked.
Cool on a wire rack before serving, then cut into 12 slices.