Gently place the gammon joint into a large stockpot, cover with cold water and bring to the boil.
Drain away the water and impurities, before covering with cold water once more and adding all the gammon ingredients. Bring to the boil and reduce to a simmer for 20 minutes per 500g (2 hours for a 3kg joint).
Remove the gammon from the water, discard the vegetables and leave to rest for 15 minutes.
Preheat the oven to 200°C and line a roasting tray with foil. Leave enough around the edges to come halfway up the joint to keep the roasting juices in.
Using a paring knife, remove the string and rind from the gammon fat leaving as much fat intact as possible. Score the joint in a diamond pattern before studding with a clove at every point the lines cross one another.
Place the gammon in the foil-lined tray, checking once more that the foil reaches halfway up the joint.
Mix the honey and mustard together in a bowl before using a pastry brush to cover the top and one side of the joint with the glaze. Place in the oven and roast for 10 minutes.
Remove from the oven and reglaze the top of the joint and the remaining side before returning to the oven with the opposite side facing the back. Roast for a further 10-15 minutes.
The joint is cooked when it's a lovely glossy golden brown colour. Remove from the oven and allow to sit for 15 minutes, saving the juices from the pan.
Warm the juices through, carve the meat and pour over the warmed juice just before serving.