Induced voltage from other circuits, pretty common. Wasn't really an issue until we started using LED lamps and they started flickering when switched off.Thanks for all your help. Last question I promise.
I am very interested in your comment about switched live. I did some more tests. With the switched live off (switch contacts open) there is still 70 volts showing between SL and neutral. Then normal 240 with switch contacts closed.
Would you expect that? Seems a bit odd to me to get 70 volts, hence why I ponder your switched live potential issue you raised?
The spark is going to come if I can get him.