Thanks all for the replies.... I have very little experience with homemade ice-cream so everything I'm doing at the moment is on a rather steep learning curve.
Have been using the Internet to look at various recipes and have found sugar percentages seem to be pretty standard.
My original try above was a no egg recipe and to be honest the kids found the 70% chocolate a bit much. I will be trying a custard based chocolate recipe in a few days from 'Ice Cream According to Østerberg - Basic recipes from Copenhagen'
The thing that's rattling around my head is that I don't add sugar to either cream (a crime in my view) nor to chocolate so what would a chocolate ice-cream with no or very little sugar actually taste like? Will definitely be giving it a go!
Also and finally I wonder if the way the ice-cream is made affects anything? Years ago I made it with a tub you froze over night but it was a faff.