[Pseudoscience-is-malarkey (OP)]

I prefer my fish grilled and especially on tacos, but what do the best "fish n chip" chefs in the UK fry them in? Are they typically fried in the same type of oil? Fried fish is popular in Upstate New York where I grew up, because Haddock is plentiful in our lakes, especially Oneida, where the family camp has been located since the 1920s. During the war, my great-grandfather managed to include preserved haddock in the care packages he sent to my grandfather and his brothers overseas.
Anyways, our fried fish and french fries (chips to you guys) are usually cooked deep in canola oil.

[Petrochemicals]

Almost all chip shops use sunflower, some use beef dripping, but it can Be a bit rich.

[Bored chemist]

From the point of view of the chip shop, the best oil is often the cheapest.
My personal preference is dripping but it's not  suitable for some people.

[paul cotter]

From a purely technical point of view in the absence of gourmet and economic arguments I would suggest a saturated oil such as coconut. All unsaturated oils are less thermostable than their saturated counterparts. Olive oil in particular is easily damaged by heat and smokes at a relatively low temperature.

[evan_au]

french fries (chips to you guys)

Belgians will always remind you that "French Fries" were actually invented by a Belgian...
- The town of Namur is in Belgium today
- But the nation of Belgium did not exist in the 1600s
https://www.tastingtable.com/740270/the-origin-of-french-fries-might-surprise-you/

[alancalverd]

Robin Hood was riding through the forest, hoping to recruit some good men and true.

In a clearing he spotted a man wearing a hooded robe, cutting up potatoes and throwing them into a pot of hot oil.

He said "Greetings, friend. Would you be the friar they speak of?"

"No, sire. I am the chip monk."

[Bored chemist]

Belgians will always remind you that "French Fries" were actually invented by a Belgian...

I strongly suspect that the South Americans beat them to it.

[alancalverd]

Most restaurant and takeaway suppliers seem to be offering palm oil.

[JesWade21]

As a member of the Southern US Fish Frying Delegation, I agree with peanut or canola. I'd also include vegetable oil as an option.

[Bored chemist]

As a member of the Southern US Fish Frying Delegation, I agree with peanut or canola. I'd also include vegetable oil as an option.

You do know that peanut and canola are both examples of vegetable oils, don't you?