Feel the OP’s pain. My house was owned by a previous ‘Jack of all trades, Master of None’. Among his greatest hits was using earth cable, and only Earth cable to wire up an extension he had built on the back of the house. I guess he ran out of live and neutral cable. Additionally, he didn’t know how to wire up double gang light switches, so none of them worked unless all the switches on the same circuit were in the same position.
The scary thing is this clown had his own business as a heating engineer, so would have been doing wiring while installing boilers, thermostats etc.