For pickled onions, combine vinegars, sugar, allspice, cloves and bay with 300ml water in a saucepan and bring to the boil. Add onions, reduce heat to medium, and simmer until softened (10-12 minutes). Cool, then refrigerate until required.
Add chips to a large saucepan of salted boiling water, and cook until edges break apart at a light touch (5 minutes). Drain, cool briefly, then lay out evenly on paper towels and refrigerate to dry (1-2 hours).
For batter, pour soda water and vodka into a bowl, add flours and mix gently by hand (it’s okay for the batter to have some lumps).
Heat oil in a deep saucepan or a deep-fryer to 180°C. Coat fish fillets in flour, shaking off excess, then dip into batter, coating the fish evenly. Deep-fry fish, turning occasionally, until crisp and golden, and centre reaches 50°C on a thermometer (6-8 minutes; be careful, hot oil will spit). Remove fish with a slotted spoon and keep warm on a wire rack with a tray underneath in a low oven. Deep-fry chips in batches, turning occasionally, until golden and crisp (7-9 minutes). Drain on paper towels and season with a good amount of salt. Serve fish and chips with pickled onions, aïoli and lemon wedges.
