Preheat the oven to 400°F (180°C fan-assisted).
Boil peeled and chunked potatoes in salted water until tender, about 15 minutes. Drain and mash with butter and milk. Season with salt and pepper and set aside.
Melt butter in a saucepan over medium heat. Add onion, carrot, and garlic, and sauté for 5 minutes until softened.
Stir in curry powder and turmeric; cook for 1 minute, stirring constantly.
Add flour and stir continuously for 1 minute to form a paste.
Gradually whisk in milk and stock to avoid lumps, stirring until the sauce thickens smoothly.
Add white fish, smoked fish, and frozen peas. Simmer gently for 3-4 minutes without boiling.
Remove from heat and stir in shrimp, parsley, salt, and pepper.
Transfer the filling to a baking dish. Spread mashed potato topping evenly and create texture by roughing the surface with a fork.
Bake for 25 minutes until the topping is golden and crispy. Let rest for 5 minutes before serving.