Rub the chicken with salt and pepper and place in an ovenproof dish (unless cooking on a barbecue).
In a large bowl mix together the oil, Worcestershire sauce, tomato puree, spring onion, chicken stock, cayenne pepper, salt, pepper and sugar. Brush the sauce over the chicken.
Grill the chicken for 30 minutes or until it is cooked through. Baste with the sauce from time to time during the cooking period.
Transfer the chicken pieces to a warmed serving dish. Pour any cooking juices into a saucepan and add the remaining barbecue sauce. Heat the sauce gently until it is hot. Pour the sauce over the chicken.