Preheat the oven to 200°C.
Boil the potatoes in salted water for 15 minutes, drain, mash, and allow to cool.
Wrap seasoned cod loin in greased foil and bake for 20 minutes until cooked through.
Flake the cooled fish into large pieces and reserve 2 tablespoons of the cooking juices.
Mix cold mash with spring onions, mayonnaise, mustard, juices, cod, crabmeat, parsley, and hot sauce.
Shape the mixture into 8 fishcakes and chill in the fridge for 15 minutes.
Coat each fishcake in breadcrumbs and chill again for 30 minutes.
Combine tomatoes, red onion, vinegar, olive oil, and parsley to make the salsa.
Fry the fishcakes in butter and oil over high heat for 4 minutes per side until golden.
Serve the hot fishcakes with the tomato salsa and a dressed salad.