A remote mains meter reading system comprises a mains system (10, 11, 13, 14), a central station (LC), and a plurality of meters (U1-U11) communicating with the central station by means of messages passed over the mains system. All of the meters act also as message forwarding (relay) units, but knowledge of the topology of the system (i.e. which meters can communicate with which) is known only to the central station. All messages are sent out by, and return to, the central station, the message format includes a list of meters through which the message is to pass. The central station can send out a variety of enquiry (SEARCH) messages to determine the system topology, assign labels to meters, etc. If the mains system includes link boxes coupling different areas together, these boxes preferably filter out messages and includes link units which controllably couple the different areas together.