Heat oil in a large saucepan over medium-high heat. Add onion, carrots cook till soft and garlic. Cook, stirring on medium heat, for 1minute or until soft. Add the flour and cook for another 30 seconds.
Add stock, celery (including leaves), butterbeans, tomatoes and basil. Bring to the boil. Reduce heat to medium. Simmer, uncovered, for 15 minutes.
Add green beans to soup and simmer for 5 minutes or until beans are tender. Season with salt and pepper. Ladle soup into bowls. Top with parsley. Serve with bread (optional).