Very good points cheers,
The pump was surging during the day, I checked the reading when I got home and it was 14,7, did not have time to explore then, This morning its now settled to 12.7 My initial thoughts were debris from tank clogging the pump, just a few jobs later in the day and will have time to explore further.
Van is Citroën Dispatch circa 2015, has a split charge relay, solar panel & charger and no smart alternator, has been pretty reliable so far TBF but as you can tell a fair few electrical possibility's.