I had the camper imported directly from Japan, the importer confirmed nothing had been done apart from standard conversion of km to miles, fog lights, etc.
I believe it will be running all lights off the 12v circuit, same for the water pump, toilet, and fridge is 3 way- 12v, 100v, gas. So best option would be potentially a step down transformer wired in directly behind the main ac power input? https://airlinktransformers.com/category/japan-uk-voltage-converters
I have ruled out all internal compartments (which has been positive as I now know where everything is, except the breaker) checked the lockers and all other obvious locations for load centre/ breaker- I will have another rummage in the external lockers this evening, and do a bit more head scratching- as well as take lots of photos in case anyone spots something obvious I am missing.