Make the sauce vierge. Pour the vinegar into a small bowl and stir in the chopped shallots and garlic. Marinate for 2 -12 hours.Just before serving whisk in the olive oil, then stir in the diced tomatoes and basil. Season with salt and pepper.
Heat the frying pan over a very high heat until very hot. Meanwhile season the scallops, dust them lightly with flour and smear them equally lightly with olive oil.
Put the scallops into the frying pan and sear them for 2 minutes on one side. Turn over and cook for a further minute. Remove from the pan and serve immediately, dribbled with the sauce vierge and a wafer or two of crisp pancetta on top.