A safety closure secured against accidental opening or opening by small children comprises a lid and a cap interconnected by a hinge made of a single piece and having a single wall, the lid having a lateral skirt, a top surface with a pouring opening and an outer lateral grip that delimits a slot for engagement with the lock provided in the cap. The continuous lateral skirt has an internal thread, and a flap or ring is provided at the lower edge of the skirt for attaching the lid to the neck of a container. The inwardly extending flap secures the lid against axial movement when the lid is rotated in order to unscrew it. The cap has a sealing plug that closes the pouring opening and an external flap from which a locking body protrudes, the locking body having a central cutout that forms a spring blade that extends outwards from the locking body.