Abstract: A cap (1) for a container having a screw threaded opening comprising an inner part (3) in the form of a screw threaded cap, an outer part (2) the inner part (3) being axially displaceable relative to the outer part (2) and biased therefrom between an unlocking and locking position, resilient biasing means (17) between the inner and outer parts, a boss (6), and engagement means (15) adapted to engage with the boss upon (6) depression of the outer part (2), such that turning the cap will unscrew it from the container wherein one of the boss (6) or engagement means (15) is located on the top surface of the inner part (3) and the other is located on the inner top surface of the outer part (2).