Clean all the seafood and cut up the fish, squid and octopus. Set aside for later.
In a large saucepan, combine the olive oil, garlic, leeks, chilli flakes and onion. Cook over medium heat for 5 minutes. Add the tomatoes, fish stock and wine and bring to a gentle boil.
Add first the clams and mussels and cook until the shells open, discarding those that don't open. Add the remaining fish and seafood and cook for 5 minutes. Stir in the parsley and season with salt and pepper. Serve by itself or over rice.