Is any cuisine, or any aspect of culture for that matter, ever not derivative? I doubt it.

The Portuguese may have been early European consumers of potatoes, but they likely got that from the Spanish, who in turn got it from Central or South America, where human consumption of this tuber originated thousands of years ago. There is no telling how many cultures it may have passed through that have been lost to the ages. And even the first potato consumers may have been inspired to eat potatoes from a prior culture of eating other sorts of roots.

From what I can find on the internet the origin is with Portuguese Sephardic Jews who fled to the British Isles in the 16th century.

Interesting, wouldn't have expected that given the relative lack of spice. As an aside, if you get to Greenwich, go get some fish and chips from the Golden Chippy. Best I've had in England.

Wait til you hear about the Italians and tomatoes!