Separate the eggs, putting the yolks in a large bowl and the whites in a smaller bowl. Whisk the whites to form soft peaks. Add the flour, cider and salt to the yolks then whisk until well combined. Fold the whites into the yolk mixture. This should result in a batter with the consistency of yoghurt. (This may vary due to the flour type used; adjust with more flour, egg or beer as needed). Pour the oil into a large saucepan to the depth of about 1 cm. Heat the pan on a medium-high heat until the oil reaches a temperature of between 170°C and 180°C (if you don't have a thermometer, drop a little of the batter in - it should sizzle gently). Cut the fish up into pieces that will fit in the pan and set to one side. Dip the fish in the batter mix until both sides are coated, then very carefully lower them into the hot fat with tongs or a slotted spoon. Fry for 3-5 minutes on each side until the batter becomes a dark/golden colour and the fish is cooked through, the repeat with the other pieces. Prepare fries according to the instruction on the package.
Serve with mushy peas and crispy fried Aviko fries.
To keep gluten-free serve with red wine or white wine vinegar as malt vinegar contains gluten!