Depending on size I always bring the joint to the boil in a pan of water, discard the water,fill up with cold water to which I add celery,carrot and onion,boil for around 15 mins a pound. I then take it out and leave to cool slightly -turn oven up to max and coat ham in mixture of Dijon mustard,maple syrup and a bit of balsamic vinegar. Bang in the oven for 20 mins or until glaze is crispy then take out and leave to rest for around 15 mins. You can skip the glaze and just coat with a bit of olive oil or butter to get a nice crispy finish. This method makes the gammon very juicy inside and crisp outside. (so they tell me I don't eat pork or ham).