Sometimes a gammon joint can be overly salty so I would put joint in a large pan cover with water bring to the boil then discard the water. Place in slow cooker with a carrot small onion (or the tops off spring onions and a stick of celery, a few pepper corns and a couple of cloves. Add boiling water from the kettle to your tast (I usually only put to half way up the joint and then turn it halfway through cooking but you could cover if you want) and cook on low for 6-8 hours depending on size. Don't discard the cooking liquid - saute and onion,carrot and celery in butter in a large pan, add stock and 250 grms of split peas you have soaked overnight -bring to boil and cook until peas are soft -you can add any scraps of ham you have left over from the joint -yum!