Pick over the crab meat to remove any residual pieces of shell then place in an attractive serving bowl.
Make the vinaigrette. Mix together the lemon juice and mustard and then gradually whisk in the oil, 1/2 tsp salt and plenty of black pepper. Stir it into the crab with the chopped herbs just before serving.
Check for seasoning and garnish with a few whole chives. Serve with plenty of crusty french bread and if you like chilled white wine.