To make the fish cakes, boil potatoes until soft; mash, but not too finely. Let cool. Cut shrimp into medium dice and sauté in melted butter along with the onion, red pepper and garlic, until the shrimp is just cooked, about 3 minutes. Add lemon juice, parsley, thyme and Cajun seasoning, and stir to combine. Drain in colander and let cool. Chop lobster; drain and stir into cooled shrimp mixture. Steam or poach haddock fillets. Flake haddock and combine with potato, shrimp and lobster mixtures. Cool then form into patties. For the coating, beat the eggs and whisk in milk. Dip patties in flour, shaking off excess flour. Dip into egg mixture until well coated, then dip into bread crumbs. Shallow fry the fish cakes in olive oil for about 3 minutes, until browned and crispy. Drain on paper towels. Make the mayonnaise by mixing all the ingredients together. Serve the fish cakes with a dollop of smoked salmon mayonnaise.