Cut crusts off the white bread and line the sides of a medium sized pudding or cut-glass bowl, by squishing the bread slices against the sides and leaving no gaps.
Next place the frozen berries and sugar (to taste) and some water in a pot. Warm over medium heat until it becomes hot and begins to boil. It should now be quite runny. Pour it into the bowl, right up to the rim. Keep a small bowl with leftover berry juice aside for porin gover any white patches the next day. Place a large plate on top of the bowl and refrigerate the pudding for 6-8 hours or overnight.
Remove from fridge and flip the pudding out onto a serving platter. The pudding should have soaked red berry juice and be completely red - if not, pour over reserved juice. You can decorate with whole fresh berries scattered on plate around the pudding.