Weigh your gammon, and allow 18 minutes per lb/40 minutes per kilo for gammons up to 9 lb or 4 kilos, and 15 minutes per lb/33 minutes per kilo for gammons over this weight.
Rinse your gammon in cold water (it should not need soaking – it is dry cured, not pressure injected with brine!) and place in a saucepan big enough to hold it comfortably. Cover with cold water. Bring to the boil and start timing from when water starts boiling. Cover the pan and reduce the heat to a gentle simmer. You can, if you wish, put a selection of whole spices (cinnamon, allspice, mace, cracked nutmeg, cloves) or a handful of bayleaves in the cooking water.
A skewer should pierce the meat relatively easily when it is done. If you are not roasting/glazing the ham, leave it in the water to cool for an hour or so (this keeps it lovely and moist and will carry on gently cooking your ham for an extra half an hour).
If you are going to glaze your ham, preheat your oven to 230ºC/Fan 210ºC/Gas 8. Drain the ham, and as soon as it is cool enough to handle, arm yourself with a sharp small knife and gently lift a corner of the skin on the ham. Peel this off leaving the fat on the ham. Place ham on a double layer of foil topped with a piece of greaseproof paper in a roasting tin (this saves on hours of scrubbing caramelized blackened sugar from your tin – trust me!) Score the fat in diamonds, and glaze as required (suggestions below). Roast for 30-40 minutes until glazed to your liking.
Stud with cloves, smear all over with mustard (Dijon or English – grainy mustard burns) and drizzle with honey or brown sugar; or
Stud with cloves and smear with marmalade. Sprinkle with Demerara sugar.
To Roast without pre-boiling: 45 minutes per kg. Preheat oven to 180ºC/Gas 4. Place gammon in a deep roasting pan. Add about an inch of boiling water to the pan. Cover with foil, and seal tightly. At the end of the cooking time, remove from oven, and raise the heat to maximum. Skin the gammon, score the fat and glaze as above. Put back into the hot oven for 25 minutes until nicely golden. Rest for 20-30 minutes before serving.