In a small bowl, combine sago and milk; cover and refrigerate 8 hours or overnight.
Grease a 6 cup pudding basin.
In a large bowl, stir together sago mixture and baking soda until soda is dissolved. Stir in brown sugar, bread crumbs, raisins, currants, dates, eggs and butter until well combined. Spoon into prepared basin. Place a piece of waxed or parchment paper over the top of the basin and secure the lid.
Place the basin on a trivet or dish in a large pot and fill the pot with boiling water to come halfway up the sides of the basin. Bring the water to a boil again, then reduce the heat, cover and simmer 3 1/2 to 4 hours, topping off water as necessary, until pudding is firm.