Paul,
That's a real tough one!.
I've been put in this situation a few times and I can't say that I enjoy it, at all.
My advice would be, if you are going to do a report, be absolutely impartial.
Just concentrate on the work that needs to be done to bring the installation back up to Regulation standard, that's the most important thing here!.
What happens after you have done your report, is entirely up to the two parties in the argument.