Today went to a fault find where the 2 way lighting is playing up. All the switching is ok but when the upstairs is off but downstairs is on, There is 50v backfeeding up the neutral to the upstairs fitting? The practical effects of this is that the bulb will flicker every so often. The customer said that by replacing the energy efficient bulb with an old style one it stopped it and the voltage disappeared? All the other lights on the circuit are showing this problem, but with voltages from 12-60v I suspect it is a loose or borrowed neutral from somewhere but tested continuity from circuit neutral to neutral bar but nothing buzzed up. The supply polarity is correct and no voltage coming in on the supply neutral. There was a cable with low IR but this has now been disconnected. Any ideas cos im stumped?