OK Erneboy & Trek. Some slight sanity. My wife is still slim enough to access the utility locker on the nearside of the van. Inside this there is a cable reel which allows us to wind in the cable (it sounds like a good idea, but in practice it is a difficult job). On that reel Frakian have installed some kind of cutout which operates when the van draws too much current. This has a reset button when the condition causing the reset has been fixed. Typically this happens if we have the air-con running and try to boil a kettle or my wife uses her hair dryer. Seemed to get this problem (the power cut-out tripping) a lot this year, but then it was very hot and we used the air-con more often.
Anyway, after operating the reset, the rapidtest result changed from live/earth reversed, to a live neutral reversed which suggests that somewhere in the lead, the polarity got changed.
So now the remaining questions.....
1) What caused the trip to operate when I haven't been using any 230V (as far as I can remember)
2) Why did the two 140Ah leisure batteries and the starter battery go flat in 5 weeks when I had the 12v switched off via the Schaudt control panel
My wife did enable the toad alarm/immobiliser (it has issues too, like the alarm going off randomly, and the courtesy light on the front passenger door flickering when the door is shut) and it did trigger one night, so that is the only device that should be operating off 12v, and that is now turned off. So I guess it is time to watch what happens once both leisure batteries are charged. When that happens I plan to disconnect them over winter. The only other device is my reversing camera which draws some power (it has a blue status light which is always on) but I believe that also operates from the engine battery.
Thanks for the advice. Now waiting for a nice spell of weather to get the cover off so I can do diagnosis on the alarm