Rinse and pick over the red currants.
Grate the zest off the lemon and orange and squeeze out the juice.
Finely chop the red onion.
Heat the currants, onions and fruit juices in a heavy based pan along with the spices and cook on a moderate heat until the fruit is tender (about 15 minutes).
Mash the fruit with a potato masher.
Pour the mushy fruit mixture into a jelly bag and leave to drain into a bowl overnight.
Next day pour the resulting juice into a measuring jug and add the port. For every 100ml/3 1/2 fl oz of liquid you will need 75g/3oz of sugar.
Put the juice mixture and sugar in your preserving pan and bring to the boil. Boil until it has reached the setting point, for more information read my post on jelly making.
Ladle into sterilised jars and pop on the lids.