Preheat oven to 325F/Mark 3. Slice leek, core apple and cut it into weges. Peel the red onion and cut into wedges. Crush garlic clove.
Heat oil in a saucepan and cook sausages until lightly browned. Add the leek, apple, red onion and garlic clove, together with the tomato puree, Worcestershire sauce, orange juice, paprika and mustard. Stir well, cover, and place in oven to cook for one hour. Serve with mashed potato and seasonal vegetables.