Drain well on absorbent paper and coat with cornflour. Sprinkle with salt and pepper. Heat oil in heavy skillet and brown oxtail on both sides removing when brown. Pour off excess fat. Dice bacon and fry for a few minutes.
Return oxtail to pot with bacon, add carrots, onion, garlic, tomatoes and hot water.
Cover and simmer gently for 3.5 to 4 hours or until oxtail is almost tender. At this stage add more liquid if necessary and season. Cover and simmer for 20 to 30 minutes. Add the butter beans and allow to simmer for 3 to 4 minutes. Serving for 4.