Heat the olive oil in a large, heavy-based saucepan set over a medium heat. Saute the onion, courgette, carrot and potato for 5-6 minutes, stirring occasionally, until they just start to soften. Stir in the tomato purée at this point and cook for 1 minute. Add the haricot beans, then cover with the stock and bring to the boil.
Reduce to a simmer and cook for 15-20 minutes until the potato and beans are softened. Stir in the tomatoes and simmer for 4-5 minutes. Ladle into serving bowls and garnish with the chopped basil and sprigs of basil leaves