Heat the olive oil in a heavy-based pot, then add the onion and celery and cook until soft (about 5 minutes)
Add the garlic and white wine and cook until most of the liquid has evaporated.
Add the stock, puréed tomato, chilli, sugar, oregano, salt and pepper and bring to the boil, then reduce the heat and simmer gently for about 50 – 60 minutes, stirring occasionally.
Add the calamari, mussels and line fish. Put the lid on and simmer for about 5 minutes until the fish is cooked and the mussel shells have opened up. Discard any unopened shells.
Stir through the cream and basil, simmer for a few more minutes and serve in large bowls with toast.