Please note no pork/ other haram meat is cooked in the oil.
بسم الله الرحمن الرحيم
If haram meat is cooked in the oil, the oil turns impure. Further whatsoever things will be cooked in impure oil it shall turn impure. Hence in the above mentioned case if the fish and chips are fried in such oil in which haram meat was cooked then as per the Shariah the fish and chips shall turn impure and it shall not be lawful to eat them. (Taken from: Imdad al-Fatwa: vol. 1, pp. 106-107, Kitab al-Taharah, pub. Zakaria Deoband)
Allah knows Best!
Darul Uloom Deoband