Abstract: A trolley locking device of the type comprising two co-operating parts, one of which is attached to each of two trolleys and whereof one part is a lock unit and the other is a key unit. The key and lock units are adapted to be releasable locked together with a coin or token is introduced into a slot in the side of the lock unit which enables the key to move a plug inside the lock unit axially to free the plug for rotation between two terminal positions thereof. The key engages the coin or token which acts as the medium for creating axial movement of the plug which is biased against such movement. Co-operating formations on the plug and lock unit prevent rotation of the plug unless moved axially against the bias applied to the plug. The coin or token can only be removed while the key and lock unit are engaged and the key can only be removed from the lock unit when a coin or token is present in the latter.