Add the gammon joint to a slow cooker and pour over the ginger ale and orange juice. If the gammon is still showing from the top of the liquid then top it up with water until it is covered.
Add the ginger, peppercorns, cloves, star anise, cinnamon stick, bay leaves and the quartered orange.
Set the slow cooker to medium and cook for 5 1/2 hours.
Once the gammon is cooked, lift it out onto a piece of foil set in a roasting tin and wrap the foil loosely round to contain the gammon. Pre-heat the oven to 200ºC and allow the gammon to rest whilst preparing the glaze. Discard the cooking liquor.
In a small saucepan add the glaze ingredients and heat to a simmer. Allow the glaze to reduce down for 3 minutes until it is thickened and sticky.
Pour half of the glaze over the gammon, allowing it to run down the sides and place in the oven for 10 minutes. After 10 minutes pour over the rest of the glaze and pop back into the oven for another 10 minutes.
Remove the gammon from the oven and allow it to rest before you try to cut it as it will fall apart if it is too hot.
Serve as part of your roast dinner.