Heat the vegetable oil in a deep fryer or large, deep pan to 350 F (180 C).
In a large bowl, whisk together the flour, baking powder, and salt.
Gradually add the sparkling water to the flour mixture, whisking until you have a smooth batter.
Dip each fish fillet into the batter, ensuring it is fully coated.
Carefully place the battered fish into the hot oil and fry for 6-8 minutes or until golden brown and crispy. Fry in batches if necessary.
While the fish is frying, parboil the chips in a pot of salted water for about 5 minutes. Drain and let them air-dry.
Once the fish is done, remove it from the oil and place it on a plate lined with paper towels to absorb excess oil.
Increase the oil temperature to 375 F (190 C) and fry the parboiled chips until golden and crisp.
Season the chips with salt and pepper to taste.
Serve the fish and chips hot, with a side of mushy peas and a drizzle of malt vinegar.
