A blade seal comprises a flexible member having a relatively thick edge opposite a relatively thin edge, and an actuator at least partially embedded in the flexible member for actively deflecting the thin edge with respect to the thick edge upon activation of the actuator. The blade seal may be fixed to an aerodynamic trailing edge of either a fixed aerofoil portion or a flight control surface of an aerofoil for sealing between the fixed aerofoil portion and the flight control surface. Also, a method of sealing an aerofoil using the blade seal.