Melt the butter in a large saucepan and sauté the onions and garlic for 5 minutes over a low heat, stirring occasionally.
Add the bacon and celery and cook for 2 minutes, stirring frequently.
Add tomatoes, wine, stock, basil and half of the parsley to the saucepan. Season to taste with salt and pepper. Bring to the boil briefly, reduce the temperature and simmer for 10 minutes.
Add the fish and cook for 5 minutes until it becomes translucent. Add the prawns and heat gently but thoroughly for 3 minutes.
Pour the soup into soup bowls, garnish with the remaining parsley and serve immediately.