The paper reviews the pioneer work carried out by the London Electricity Board, leading up to the installation of a mains-borne signalling system for off-peak load switching in a large council housing development in the London Borough of Brent. It shows how technical liaison between a manufacturer and an area board has contributed to the evolution of a secure and viable scheme. Sensitivity and stability are discussed using different signalling methods that employ solid-state devices to modify the 50 Hz waveshape. Results of the trials on interconnected and radial low voltage supply networks are presented, indicating that the type of urban low voltage (l.v.) supply is unlikely to affect the efficiency of the signalling systems. An improved signalling technique, proposed by GEC Measurements and used in the Brent installation, is described.