Grease an empty fruit can (or cans) which will hold 3-4 1/2 cups.
Slowly bring plenty of water to the boil in the bottom of a steamer, or enough water in a large saucepan to come halfway up the can or cans.
Heat the milk and syrup together until the syrup has dissolved; cool, then stir in the baking soda.
Place the flours, salt, sugar and oats in a large bowl and stir in the raisins and chopped walnuts.
Pour the cooled milk mixture into the dry ingredients and quickly mix together to give a fairly soft batter.
Spoon the mixture into the prepared can orcans until two-thirds full.
Cover tightly with foil then put in the steamer or on a rack in the saucepan.
Steam for about 2 hours until the bread is well risen and firm.