Heat the vegetable oil and beef dripping in a deep fat fryer to 170°C.
Fry the potato batons for 2-3 minutes until tender but not browned.
Drain potatoes on kitchen paper and increase oil temperature to 190°C.
Mix yeast, salt, and sugar in a bowl until combined.
Whisk in tonic water, flour, vodka, and vinegar and leave until bubbling.
Coat cod fillets in batter and fry for 3-4 minutes until golden-brown.
Remove the cod and drain on kitchen paper.
Fry chips a second time for 2-3 minutes until crisp.
Simmer vinegar, spices, and brown sugar in a heavy-based pan.
Add tomatoes, garlic, and remaining ketchup ingredients and bring to a boil.
Simmer the ketchup for 30 minutes while stirring occasionally.
Blend the ketchup until smooth and pass through a sieve.
Serve the cod and chips with the homemade ketchup.