I can eat quite a lot of carbs now I've got things under control, but potatoes aren't one of the things I can eat: it doesn't seem to matter if they're boiled, mashed, roasted or chipped: they send my blood sugar sky high
I have roast celeriac instead of potatoes now
It never ceases to amaze me how different we all are.

Potatoes aren't great for me, but they are FAR better than any of the grains. Those spike me to the skies, while potatoes are kind of doable, in small portions.
Whenever we go out I indulge in maybe 1/4 to 1/3 of a portion of chips, whereas I reject anything like bread, breadcrumbs, and gloopy sauces thickened with flour.
So,
@Terryrhino
In your fish and chip scenario, I will peel the batter off the fish, and eat about 1/4-1/3 of the chips, and be OK.
Of course, I would be better with a salad and no potatoes at all, but hey, I'm human! (well, sometimes)
- and given the choice of different forms of potato, I would go for chips, roasties and dauphinoise potatoes over baked, boiled or mashed, simply because the fat slows down the spike. Terrible, innit? FORCED to eat chips rather than boring jacket pots. Such a hardship.
Mind you, I still avoid potatoes on principle, unless we are out, and I am having a treat. Never buy them. And never cook them myself. That would be a very slippery slope!