Place the mulberries in a glass and pour the vinegar over.
Leave to stand for at least 24 hours, stirring and pressing the fruit regularly, to extract the juices. Strain the liquid into a large saucepan and bring to the boil. Add the sugar, stirring until it is completely dissolved, then add the honey, stirring well. Bring back to a boil and boil hard for 5 minutes. Allow to cool completely.
Originally this syrup was bottled and stored, one tablespoon being added to a glass of hot water to form a bedtime drink. However, the syrup can easily be frozen in ice-cube trays and then stored in bags in the freezer to be used when required.