Carefully rinse all the berries; de-stem the currants – setting 4 little clusters aside for decoration – and put them in a small heavy-bottomed saucepan with the raspberries. Add the sugar and water, bring to the boil and simmer for roughly 15 minutes, stirring from time to time. When it has cooled down, use the back of a spoon to strain the mixture through a sieve into a bowl, and then divide the pulp you obtain between 4 glasses. If there is enough room, put everything in the fridge to cool for 10-15 minutes. Just before serving, add 5-6 ice cubes, 50 ml of gin and 100 ml of tonic water (both chilled) to each glass. Stir delicately and decorate with the fruit you set aside; the little clusters of red currants look perfect “sitting” on the rims of the glasses.