Preheat the oven to 190℃ (170℃ fan)/375°F/gas mark 5. Lightly grease and line a 900g (2lb) loaf tin
Cut a few pieces of the rhubarb into short lengths and set aside. Cut the remaining rhubarb into small dice.
Beat 175g (6oz) butter and 175g (6oz) sugar together with a wooden spoon or electric beaters until very pale and fluffy.
Add the eggs one at a time, beating well after each addition. Add a tablespoon of the 200g (7oz) self-raising flour with the last egg.
Add the chopped stem ginger, then sieve in the remaining flour and 1 teaspoon ground ginger into the bowl Fold in along with 2 tablespoons of milk.
Fold in the prepared rhubarb and spoon into the prepared loaf tin and level the top. Place the reserved strips of rhubarb on top and sprinkle with a little demerara sugar.
Bake in the centre of the oven and about 1 hour until golden risen and a cake skewer inserted in the centre comes out clean.
Allow to cool in the tin for 5 minutes before transfering to a wire rack to cool completely.