Heat 3 inches of the oil in a deep fryer to 325 degrees F. Alternatively, use a deep heavy skillet.
Peel the potatoes and cut them into chips (that is, fries) about the size of your index finger. Put the potatoes in a fryer basket and lower into the oil. Fry the chips for 2 to 3 minutes; they should not be crisp or fully cooked at this point. Remove the chips to a paper towel-lined platter to drain.
Crank the oil temperature up to 375 degrees F. In a large mixing bowl, combine the flour, baking powder, salt and pepper. Combine soda water and egg and pour into the flour mixture. Whisk to a smooth batter. Spread the rice flour on a plate. Dredge the fish pieces in the rice flour and then dip them into the batter, letting the excess drip off.
Put the chips in the bottom of the fryer basket and carefully submerge in the hot oil. Carefully lower the battered fish into the bubbling oil on top of the chips. Fry the fish and chips for 4 to 5 minutes until crispy and brown. Remove the basket and drain the fish and chips on paper towels; season lightly with salt. Serve wrapped in a newspaper cone with malt vinegar and/or tartar sauce.