In a blender or food processor, puree the blueberries along with a teaspoon of sugar - set aside
In the blender puree the red currants along with a teaspoon of sugar - set aside
Pour the three mixtures (red currant, blueberry, yoghurt), alternating, into popsicle moulds to create about 5 layers of the mixtures
With a thin knife or skewer insert into mixture and swirl together slightly in an up-and-down motion
Insert ice-block sticks and freeze until solid