Put the tomatoes in a saucepan with the stock, 2 tablespoons of the oil, the garlic, sugar and basil and bring gradually to the boil. Cover the pan, reduce the heat and simmer gently for 30 minutes.
Crumble the bread into the soup and stir over a low heat until it has thickened. Stir in the vinegar and the remaining oil and season with salt and pepper to taste. Serve immediately or leave to cool to room temperature.