and considered doing this with just the switch turned off. After turning off the switch I checked the voltage with a meter in A/C mode. It was 140V which I thought a tad high. When I turned the switch on the reading was 230V as expected (in the UK). So I turned off the lighting circuit at the consumer unit which brought the voltage to less than 1V as expected. So what I can't work out is where the 140V is coming from ? All the lights work independently so I don't think it is a series wiring thing. Any ideas or trouble shooting tips ? This is the electricians forum isn't it ? E.