Put the peppers, skin side up, and the tomatoes, skin side down, on a baking sheet under a hot grill and cook for 8—10 minutes until the skins of the peppers are blackened. Cover the peppers with damp kitchen paper, leave to cool, then remove the skins and slice the flesh. Leave the tomatoes to cool, then remove the skins.
Heat the oil in a large saucepan, add the onion and carrot and fry for 5 minutes. Add the stock and the skinned roasted peppers and tomatoes, bring to the boil and simmer for 20 minutes until the carrot is tender.
Transfer the soup to a food processor or blender and process until smooth, in batches if necessary. Return to the pan and heat through gently. Stir through the crème fraîche and basil, season well with pepper and serve.