To be honest with you all, I tend to dislike deep frying myself, not because it could be greasy or whatever but because I am ever so clumsy. With oil which can reach temperatures from 177 degrees Celcius to 205, a little mistake can give you a serious burn or even a trip to the hospital. So even if I do like a good fish and chips, I do tend to order it rather than do it myself. By the way in the 1860's the first fish and chips shops were created in London.
For a national dish it does have more than a century and a half of credential. However the deep frying of fish dates back from much longer especially in Spanish and Portuguese comunities. As for the French Fries history are hotly ( It is the time to say it when we speak of hot oil) disputed between Belgium and the French.
Deep fried fillet of Trout, with Baby Potatoes and Broad Beans
Despite the history of it all which is very interesting, my curiosity is turned more on the type of batter used for fish or veg or fruits or else. I remember the time when my Mum was doing apple beignets for us with great delight.
Speaking of batter to coat the ingredients to deep fry, I made many experiments. By personal taste I like a light batter, and if I have to chose my personal choices I would say, either sparkling water, cider or a very decent nice ale...
A good Ale does help to give any batter a little oomph.
Now there is something very inconvenient about deep frying: You have to think of how to dispose of your oil. How many times can you use or re-use your oil? When is it safe and when it is beyond health safety? Then you can not, never pour it in a drain. Let your oil cool down, pour it in a bottle which you can seal and give it to garbage/council collection to be dealt with safely.
The choice of oil for deep frying is all yours. For me I tend to go for vegetable oils, Sunflower oil or Rapeseed oil. Canola oil is the best. The oil you choose needs to be neutral in general. You want to feel the effort you did impart to your Batter. It is all about the taste. But also to keep the full flavour of the ingredient you are deep frying.
Sunflower Oil comes in large bottle sometimes which is convenient for deep frying.