Place the chips in a large, heavy-based pot or casserole dish and pour over the sunflower oil until it covers them. Place over a high heat and bring to a steady boil. Reduce the heat to medium and cook for 15 minutes before gently moving with tongs to loosen any that are stuck to the base. Continue to cook for a further 5 minutes or so or until they turn golden-brown.
Remove with a slotted spoon to a baking tray lined with parchment paper. Season generously with sea salt and keep warm in a low oven. Top the pot or casserole dish up with more oil if needed and bring it back to temperature over a medium-high heat. It needs to be very hot when you start to fry the fish.
Cut the fish fillets into thick strips.
Add a couple tablespoons of flour to a dish and season well with salt and pepper. Toss the fish in the flour, shake off the excess and set aside.
Place the flour in a large mixing bowl, make a well in the middle of it and pour in a little beer and mix through, keep adding the beer and mixing until you have a smooth batter.
Season generously and then drop a little of the batter into the hot oil. If it floats and puffs up, the oil is hot enough to fry the fish. Working beside the pan, dip the fish strips in the batter one at a time and then into the hot oil. Make sure not to overcrowd the pan.
Cook for about 4 minutes until golden-brown, turning halfway through the cooking time. Once done, remove the fish from the pan using a slotted spoon and place on a plate lined with some parchment paper.
Season with a generous sprinkle of sea salt and vinegar, and serve with lemon wedges and a good helping of chips.
Notes
Top tip here is to not overcrowd the pan. Some fryers are big enough but most of us will have to do this in batches. Keeping the oil at the right temperature is the only way to ensure crispy chips and perfect batter on the fish.