Mix cornflour, plain flour, and salt in a large bowl.
Whisk in the ale and vinegar until the batter reaches a smooth double cream consistency.
Heat sunflower oil in a deep saucepan to 180°C.
Season flour with salt in a food bag and coat each fish fillet thoroughly.
Dip a floured fillet into the batter and gently lower it into the 180°C oil.
Fry two fillets at a time for 5-6 minutes until golden-brown and crisp.
Drain the cooked fish on kitchen paper and repeat with the remaining fillets.
Serve the hot fish immediately with freshly cooked chips.