Thank you Lady Penelope and JimmyT very much for your advice.
The OC has now managed to get him to go through the ‘complying development’ route, seeking approval from a private accredited certifier and to submit a letter from the Council regarding no change to the strata plan being required.
Once he has all the information, he is required to submit to OC for further consideration. We expect to use the by-law process to limit our liabilities and costs. We might need to hire solicitors when required.