We had a similar case - also in Lower Hutt and got good backing from the LHCC.  We started a job for a customer installing a solar system etc.  The customer was an engineer.  He phoned on the Monday to say not to bother coming back as he had finished the job himself.  We contacted the Council and the manufacturer - the council so that a notice could be put on the consent saying we did not complete the work but that the homeowner had completed it and we would not be responsible for anything he had touched and the manufacturer so they could alter the warranty as it stated it had to be installed by one of their approved installers.  The council wrote to the customer and told him that they would withdraw the consent and the manufacturer told him he had voided the warranty.  Apart from the customer having enough knowledge to be dangerous he was an ok guy and paid his bill - we still can't fathom why he wanted to finish the job himself - maybe he was bored over teh weekend.  The moral of this story is that the Council will support tradesmen if they work with them - we were really pleased with how swiftly the Lower Hutt City Council moved on this.  Bouquet for them and their plumbng inspectors!!  I too am thrilled they are asking for licenses.  Long may it continue.