There is very little that one can buy from a UK or Ireland fish and chip shop that is intrinsically unhealthy. The Health Gurus will insist that deep-frying in lard, vegetable oil of beef tallow (dripping) is nasty, but if fast food such as fish and chips are eaten as part of a balanced diet, I can foresee no harm.
Fish, even deep-fried, contains calcium, protein, valuable anti-oxidants, vitamins and a host of essential minerals. Chips, made from real potatoes (rather than the re-constituted Russet Idaho and such varieties used in some manufacturers Oven varieties) are rich in vitamins and protein. One can get just about every nutrient needed by the body by eating potatoes.
Fish and Chips, Saveloy and chips, Sausage and chips provides a good meal. One gets a good balance of fats, proteins, vitamins, carbs and minerals. Foie Gras is pure fat, Salad is seriously deficient nutritionally, the fine French Sauces are full of butter and often cooked to death.
Eat fish and chips and enjoy them!
I'm a qualified chef