Place the whole oranges and salt in a large saucepan with enough cold water to cover and bring to the boil. Reduce the heat to medium, cover and cook for 40 minutes. Remove from the heat, drain and stand until the oranges are cool enough to handle.
Meanwhile, combine the brown sugar, golden syrup, vinegar, water, cardamom pods, peppercorns, mustard seeds, cloves and allspice in a medium saucepan and bring to the boil. Remove from heat.
Cut the oranges into quarters with a sharp knife and then cut roughly into 2cm chunks. Return the oranges to the saucepan and pour the syrup mixture over. Bring to a simmer over medium heat and cook, uncovered, for 30-35 minutes or until the orange rind is tender.
Remove from heat and stand for 3-4 minutes before spooning into hot, sterilised jars (see note), pushing the mixture down into the jars with a clean spoon to expel air bubbles. Seal the jars, invert for 2 minutes and then stand uptight. Allow to cool, then label and date.
