Place the gammon in a very large saucepan and cover with water. Heat until the water is at a rolling boil.
Remove the gammon and pour out the water, giving the pan a rinse.
Place the gammon back into the pan and add all the ingredients (except the ones for the glaze). Top up with water to cover the gammon.
Bring to a boil then reduce the heat to a simmer, cover and cook for 90 minutes (one and a half hours).
Remove the gammon (which is now called ‘ham’ since it is cooked) from the liquid and allow to rest whilst you prepare the glaze.
Pre-heat the oven to 200°C / 180°C fan assisted / gas mark 6 / 400°F.
Remove the string from the ham. If it has a thick outer skin on top of the fat then cut that away so only the thick layer of fat remains beneath.
Make a large diamond pattern into the fat with a very sharp knife, being sure not to pierce the meat. Then place a clove into each diamond.
Blitz the ingredients for the glaze in a small bowl using an immersion blender until smooth. Then brush half of the glaze all over the ham.
Place the ham in the oven on a foil lined roasting tin with a ladleful of the cooking liquid at the base of the pan. Roast for 30-35 minutes, basting the ham with the rest of the glaze twice (after 10 and 20 minutes) during the roast.
Remove the ham from the oven and allow to rest for at least 10 minutes before carving and serving.