Season the chicken with salt and pepper. Heat butter and oil in a large heavy-based saucepan over medium heat. Fry to seal chicken pieces until brown on all sides. Remove from the pan and set aside.
Stir the flour into the dripping and reduce the heat to low. Cook, stirring frequently, until the roux (flour and fat) turns dark.
Add the onion, celery, green pepper and garlic to the roux. Cook, stirring constantly, for 5 minutes.
Stir in the stock, water, Worcestershire sauce, chilli, bay leaf, thyme, allspice, cloves and some black pepper. Heat to boiling, then reduce the heat and simmer, uncovered, for 30 minutes.
Add the chicken pieces and continue to simmer, uncovered, for 1 hour, skimming the surface if necessary. Discard the bay leaf.
Add the mussels, parsley and chives and cook for a further 8 minutes. Serve with rice.