Place the gammon into a large lidded saucepan, cover with cold water and bring to the boil over high heat.
Drain water then add fresh cold water (enough to cover the joint). Add the bay leaves, peppercorns and 2 strips of grapefruit peel. Bring to the boil once more then turn down to a simmer, and simmer for 20 minutes.
Preheat oven to 190.
Drain the gammon, saving half a cup of the liquid (the rest can be reserved for future soups and stews) and place in a large roasting dish.
Add the sugar and the juice of the grapefruit to the cooking liquid and stir until the sugar dissolves, then brush it over the joint evenly.
Place in the oven for 20 – 30 minutes until golden brown all over.