A well plug having a flexible expandable sealing (330) and a metallic anchor (350) which can be moved radially out or in by rotating a leadscrew (170) in opposite directions. The well plug has a ball valve in a central longitudinal passage, which is kept open whenever the leadscrew (160) rotates. This increases the accuracy when setting the plug, and reduces the risk for the plug moving uncontrolled in the well bore during setting or retrieval. The ball valve can be opened or closed by rotating a transmitting shaft (120, 140) within an angle of free motion, before the leadscrew is pulled along in the rotation. A ball valve for high pressure applications is also shown.