Before you start, place 2 saucers in the freezer and sterilise jars (see notes).
Wash the oranges and lemon to clean and remove any wax coating (even organic fruit can have a natural wax coating). See notes below.
Pierce a hole in the end of the oranges and lemon (I used a large metal skewer).
Place the fruit and water in as small a pan as they will fit (the water won't cover the fruit fully) and cover with a lid.
Bring to the boil and then boil gently until soft (about 1 ¾ hrs) and test with a skewer. Do not lift the lid at any point before the end.
When the fruit is easily pierced with a skewer remove from pan with a slotted spoon. Cut fruit it into quarters, remove pips and slice thinly.
Transfer the hot liquid to a large preserving pan and add the cut up pulp.
Place a few saucers in the freezer to test for set.
Bring the liquid and pulp to the boil, then turn down heat to low and add the sugar. Stir with a wooden spoon until sugar dissolved (until no crunching sounds can be heard).
Turn heat up to high to bring mixture to a rolling boil (see photo in post above) and time for 13 minutes (or reaches 105°C on a digital thermometer), still stirring. You can tell when jam is nearing readiness as a drop of marmalade will cling to wooden spoon as you pour it off.
Test a few drops on a chilled saucer and put in the fridge for 30 seconds. If it forms a gel like crinkle when pushed it is ready. Otherwise carry on boiling for 2 minutes intervals and re-testing (mine took 15 minutes).
Strain the marmalade through a large metal sieve placed over a clean bowl, squeezing the rinds with the back of a spoon. Or skip this step for marmalade with shreds.
Push any scum to the side of the pan and remove with a metal spoon.
Use a ladle and jam funnel (if you have one) to fill the hot sterilised jars and screw on lids immediately.
Makes at just over 3 x 280 ml (9 oz) jars.