Using a potato peeler pare off the coloured part only of the orange zest then, using a sharp knife, cut this into little shreds. Squeeze out the orange juice.
Put the prunes, orange juice and zest i a bowl. Add 1 pint of water, stir wverything around and set aside for 2 hours.
Pour the contents of the bowl into a saucepan. Add the sugar and simmer very gently for an hour without a lid- it should only just simmer so check from timre to time.
At the end of the cooking time tip everything into a serving bowl and add the port while still hot. Allow the prunes to cool completely in this liquid then chill beforte serving as above.