Wash oranges well; pare 1 orange very thinly and steep peel in port for 1 hour. Soak gelatine in half the water; stir over heat until dissolved.
Slice remaining oranges in half, and scoop out pulp and juices, reserving orange shells. Remove pips from pulp. Combine juice and pulp of all oranges and the lemon with sugar and remaining water. Strain dissolved gelatine and port into orange m