Actually I thought that rather clever allowing a single direction indicator warning lamp to be used when either direction indication selected. The warning lamp being wired across left and right indicator feeds and the circuit return through the bulbs of the non-selected indicator circuit. Current flow through say a 3 watt warning bulb and the combined 42 watts of front and rear indicators. The significantly higher resistance of warning bulb allowed most of the battery volts across it with current flowing in one direction or other when a selection made. I believe it was common practice in British cars of the period allowing use of a two pin indicator flasher and no diodes.
Lucas and others got up to all sorts of inventive tricks during that period. Parking lights, still required in unlit areas, achieved by ignition off indicator selection to illuminate one side or the other. Driving lights provided by dip beam headlamp filaments in series etc. Earlier still a Lucas DB10 flasher relay box that allowed each stop light to double as flashing rear indicator when selected, and I believe fitted to some early Morgan's.
