Salt and pepper oysters and dredge in flour. Grill them on a lightly buttered grill (or saute lightly in a heavy skillet) until browned on both sides. Set aside and keep warm. Heat in saucepan on low, without boiling, the lemon juice, A1 sauce, Worcestershire sauce and sherry. Blend the 2 tablespoons of flour with the water and add to sauce to thicken. Place oysters on a platter and pour about a spoonful of sauce on each one. Run the platter briefly under the broiler to brown before serving.