1. Cut the clean fruit in half and squeeze out the juice, setting the pips aside.
2. Remove the membranes from the tangerines, with a teaspoon, and put them in a bowl, together with the pips and 1/2 pint of cold water.
3. Cut the tangerine peel into narrow strips (there is no pith on these fruits).
4. Peel the lemons and add the pith to the pips.
5. Leave the peel, the fruit juices and the remaining water in a large bowl for about 8 hours.
6. Bring the contents of the large bowl to the boil, with the fruit membranes, pith and peel tied in muslin.
7. Boil steadily for about 1 hour or until reduced by half, then remove the muslin bag and add the sugar.
8. Boil until set.