the lock bolt back against its spring loading as the door reaches its fully closed position the lock bolt is forced outwardly by its spring loading to locate behind the side face 42 of catch limb 32 at the same time the dead lock actuator bar 27 of the lock enters slot 26 and strikes a ramp surface 55 formed in front plate 22 at the end of the slot so as to be actuated to move the dead lock pin within the lock in the usual manner as will be described below catch member 16 can be locked in position so that face 42 of its limb 32 acts as a locking face to prevent opening of the door however catch member can be released so that it can be pivoted about pivot pin 28 to allow release of the door in the manner shown in fig5 the locking and release of catch member 16 is achieved through a detent mechanism comprised of a lever 43 and a keeper member 44 which is controlled by means of a solenoid 46 lever 43 is in the form of a long bar provided at one end with a bore 48 to receive a pivot pin 47 by which it is pivotally mounted on casing 18 it is disposed within casing 18 immediately behind catch member 16 and it extends longitudinally of the catch member.