This subject is actually the reason I found and joined this forum several years ago.
The one time I've fallen foul of this Part P/3rd party inspection nonsense was on a pair of barn conversions where all out war had been declared between the owner of the barns and the local building control.
The 3rd party inspector was the owner of a local electrical contracting company, who was absolutely insistent that my plate switches inside the bathroom was unacceptable. We had the regs on the table in front of us, but he still wouldn't give way. He just couldn't see what the wording actually said, rather than what he wanted it to say.
Doubting my own sanity, I joined this forum, intending to post the question, but a search revealed a recent thread discussing the exact same thing, and showed that I was correct.
Switches went in the bathroom, and presumably he submitted his EIC to building control. Never heard any more about it.
When it came to the second conversion, I just submitted my own EIC as normal.