Well only just got home from the job again, it turns out there is 11 rooms being fed off one 5amp fuse, and most rooms have between 2-4 wall lights, Today we managed to check all the upstairs lights, and find the feed to the first light, it then branches left and right to other fittings, the upstairs is fault free apart from testing the feed cable which we have still to find the other end of.
We have narrowed the fault to 3 rooms downstairs (or maybe the upstairs feed cable) all of which have wall lights so there is somewhere a JB under the floor boards for poss 3 rooms, not good news as the cottage is 300 years old!
Voltage today between earth/neutral was up to 175 volts, and readings where between earth/neutral 0.02 megohms, and phase/earth 6.8 megohms.
Just waiting for customer to decide on when they are happy for floor boards and carpets to come up!!
Oh the joys
Richie