so it was aTT supply, some idiot fitted an earth into a non-connected earth termianl & never tested it, DNO have came and replaced the head and rleft the earth in a terminal block on its own and not connected. and since it was never linked, he has left it in the same condition as when he arrived.
your only real option is to fit a rod since your supply is TT
your only real option is to fit a rod since your supply is TT