Place gammon, lemon, orange, apple, cinnamon, onion, chillies, and two star anise into a large lidded saucepan.
Cover with water, bring to a boil, then simmer for 2 hours until tender before cooling in the liquid.
Preheat the oven to 230°C.
Melt marmalade, honey, mustard, remaining star anise, and cloves in a small pan to create a glaze.
Score meat fat in a criss-cross, apply glaze, and roast for 20 minutes, basting frequently.
Boil potatoes in salted water for 15 minutes, drain, and toss with butter and seasoning.
Heat milk with clove-studded onion halves until simmering, then remove from heat to infuse.
Melt butter, whisk in flour, and gradually add infused milk to create a smooth, thick sauce.
Stir in cream, cook for 2 minutes, season with lemon juice, and add chopped parsley.
Serve carved gammon over buttered potatoes with parsley sauce on the side.