Earlier this year the UK PM mentioned that she scrapes the mould off jam commenting that "the rest is 'perfectly edible'".
The FSA comments on the topic: "While it is possible that removing the mould and a significant amount of the surrounding product could remove any unseen toxins that are present, there is no guarantee that doing so would remove them all."
The USDA has a handy table and comments on jam:
Handling: Disgard. Reason: The mold could be producing a mycotoxin. Microbiologists recommend against scooping out the mold and using the remaining condiment.
The topic seems to split opinion; I've heard some people claiming that to be ok, some say remove an inch from the top and the rest is ok, some say dispose of the whole jar, and to some it will depend on the type of jam, mould and age. I remember my food safety module professor telling us that mould can root through food so the whole thing should be chucked.
Interested to hear the thoughts of the food safety savy folks here on the matter...