Try reading post #9 for a start or did you miss thatSo instead of getting personal, how about you tell us your theory!
Checking the voltage a few other properties is all useful info to the DNO
You identified the local sub did you look around it for any sign damage
What voltage was on the stairwell lights
You accepted the DNO's response that having isolated the property at the main switch it was safe, what about the meter was that isolated or did a 240v meter still have 415v connected to it creating a potential fire hazard, how many other apartments within the building and adjacent properties unknowingly also had potential fire hazards because of the over voltageNot quite sure how I can be "out of [my] depth" when the fault is on the supply side and acknowledged it's the DNO's responsibility and contacted them.
If the DNO didn't want to turn out I would have been talking to the fire brigade due to the potential fire hazards the fault might create I'm sure the fire brigade would get a response from the DNO
No and see aboveIs that a windup? What more could he have done?
Maybe I approach things differently, over the years I have reported many network faults to the DNO's local to me, some of the faults are not that apparent but they are faults to which they respond and repair, yes I have a good working knowledge of three phase and how the DNO network is constructed and operates and it all helps when reporting a fault, had quite a few DNO guys on the ground comment that it's a pity more electricians are not as clued up and report faults
I suppose it was good that it was a TNS supply could have been very interesting on a TNCS Supply