Grill the sausages until browned and just cooked. Meanwhile heat the oil in a large saucepan, add the onion and fry for 5 minutes until softened and just beginning to brown. Add the garlic, potato and carrot and fry briefly, then mix in the tomatoes and lentils.
Pour in the wine and stock, then add the cranberry sauce, tomato purée, allspice and herbs. Season well with salt and pepper then slice the sausages and add these to the pan. Bring to the boil, stirring, then cover and simmer gently for 1¼ hours. Taste and adjust seasoning if needed.
Ladle the soup into bowls and serve with French bread croûtons (see