I was once conned into a meeting without a witness when I worked in a Scottish secondary school. I managed to handle it.
I never allowed myself to be put in that position again. Later - prior to a tribunal where the senior manager responsible found himself in trouble for bullying and other matters - the area union rep was aghast when he heard about the meeting. Apparently, if that had been in the tribunal evidence it would have been an open and shut case.
By then, I no longer had the paperwork, so it was never addressed in the tribunal. (I had been formally interviewed, but had blanked out that particular incident.)