A tube clamp having first and second opposed jaws (1012, 1014) joined by a hinge (1016), the jaws (1012, 1014) movable between open and closed positions, the tube clamp adapted to attach to a flexible plastic tube (1024) so that the tube (1024) passes between the jaws (1012, 1014), whereby the flow of fluid through the tube (1024) is permitted when the jaws are open but is blocked when the jaws are brought together to the closed position to pinch closed the tube there-between, and locking means (1048,1036,1042) to effect substantially permanent and irreversible locking of the jaws (1012, 1014) in the closed position.