This invention relates to a coupling plug lock assembly 2 for controlling access to a coupling plug 1. The lock assembly 2 includes a housing 9 for receiving the plug 1, an actuator 10 moveable between a latch position and a release position, and a lock means 17 for locking the actuator in the latch position. The lock assembly 2 is intended for obstructing access to the plug 1 for discouraging unauthorized access to the plug 1.