Place the gammon in a lidded pan, cover with water, bring to boil, and drain.
Add fresh water, onions, carrots, celery, bay leaves, and peppercorns, then boil again.
Simmer covered for 20 minutes per 500g.
Remove the gammon from the liquid and let it cool for 15 minutes.
Preheat the oven to 200°C and line a roasting tin with foil.
Remove the rind, score the fat in diamonds, and stud each center with a clove.
Place gammon in the tin and brush with half of the honey-mustard mixture.
Roast for 10 minutes, apply the remaining glaze, and roast for 10-15 more minutes.
Rest the meat for 15 minutes before carving.
Warm the collected roasting juices in a pan and spoon over the sliced meat.