A latch has a displaceable latching element in a housing for engagement with a separate striker arm to be latched behind an engagement shoulder of the latching element. The housing mounts a cylinder lock to receive a key from the front. A rotor is mounted on the rear of cylinder lock and rotation of the key rotation the rotor to drive a locking element to engage and lock the latching element. Therotor may also be axial displaceable against spring biasing responsive to a rear unit pushing element whereby unlocking from a rear cylinder lock may rotate the rotor to unlock and pushing causes thelatching element to be displaced against its biasing to release the striker arm. Embodiments include a gravity biased and manually opened latch and a spring biased self-locking embodiment.