A mechanism comprising a first component having a first magnetic part, a second component, and a third component having a second magnetic part, the third component being moveable relative to said first component in a given direction to effect connection and or disconnection of the first and second components by causing interaction of the first and second magnetic parts, wherein, when connected, the first and second components are able to move relative to one another in said given direction. The mechanism further comprising a fourth component for engagement with said first component to prevent movement of the third component relative to the first component as a result of relative movement of the first and second components, thereby to prevent unintended disconnection of the first and second components.