Preheat the oven to 180C/350F/gas mark 4.
Place a flameproof casserole dish over a medium heat and add 1 tbsp of the oil. Add the merguez and cook them on all sides until golden brown. Remove them from the pan and set aside.
Add the remaining 1 tbsp of oil and then the smoked bacon or pancetta and the chorizo. Cook over a medium heat until they have both browned and the chorizo has released its oils. Add the onion and garlic and sauté for 3-4 minutes, until the onion has softened.
Stir in the smoked paprika and cook for a couple of minutes to release the maximum flavour. Add the wine, bring to the boil and cook until it has reduced by half. Now add the tomatoes, butter beans, browned merguez and the chicken stock and bring back to the boil. Cover the dish and place it in the preheated oven for 40 minutes, or until the sauce has nicely reduced.
Remove the casserole dish from the oven and add the chopped tarragon. This is meant to be quite an oily dish, but you can drain off some of the chorizo oil if you like. Serve immediately with some hunks of good crusty bread.