Make a marinade by combining soy sauce, marmalade, sugar, crushed garlic and ginger in a microwave safe bowl. Heat for about 30 seconds to 1 minute in a microwave until runny. Once it has cooled down a bit, massage into the pork using your hands. Cover and set in fridge for 12-24 hours.
Preheat oven to 200 degrees C / Gas mark 6. Place the pork joint in a roasting tin but reserve any marinade for basting while cooking.
Cook for 40 minutes (without letting the outside burn - if necessary, cover with foil and baste with marinade sauce every ten minutes).
After it's evenly browned, remove from the oven and completely wrap up the pork with aluminum foil. Set aside for 30 minutes to 1 hour to rest before slicing.
If you have any marinade left, bring to the boil in a saucepan and pour over sliced pork.