Just trying to re-ignite this one as I'm back there tomorrow to have a go at it.
I'm going to start by taking all the LED lamps out of the circuit, and test again for the voltage. If it is still present (which I'm sure it will be) I'll then start taking the circuit apart.
The thing that is bugging me is that with ALL the light switches of the circuit off, I still get 74v at this particular down light fitting. And I also get approx 58v at the bathroom light fittings.
As said before all the neutrals are in Wago's, the wiring is new, all the conductors are meggering at >499 (I tested at 1000v to make sure). I've meggered the switches, taken the switches off and connected the wires into Wago's.
ANY ideas would be good just for me to try them. The more I think about it the more confuddled I get.
Many thanks for taking the time to read this.