Dice the gherkins into small squares, then finely chop the capers; add the parsley and mix together in a bowl. Add the mayonnaise and lemon juice and stir to combine. Cover with plastic wrap and place in the refrigerator to chill.
Heat the oil in a deep fat fryer to 350 degrees F. Mix the flour, baking powder, desired amount of turmeric, salt and pepper and vinegar in a bowl. Slowly add the water, whisking until the batter is smooth and the proper consistency.
Put flour in a pie plate or shallow bowl. Dredge the fish in the flour, then dip into the batter. Add the fish to the oil and fry until golden brown, about 5 minutes.
Peel the potatoes then cut into large potato strips. Fry the French fries at 350 degrees F until golden brown, 7 to 10 minutes. Season with salt and pepper.
Serve fish and chips hot with tartar sauce and any other condiments you like, such as hot pepper sauce, ketchup or the like.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.