They don't have to write a report because the theory is what is wrong about ensuring a car is roadworthy? Ambiguous? Defect it and let the owner find out if it should have been!
Good luck with it. Last time I was defected the cop was a real prick about it, I was idling through a roundabout in 3rd minding my own business. I was polite but he certainly wasn't, torch in the car and face asking me what things are doing in the car, etc. This was ACT. Most of the time cops are polite but you remember the bad ones, especially if they give you a defect.
Time before that was a vehicle inspector in a car park! Should have just driven off.