I had a disciplinary hearing yesterday, and I have been very glad that I have paid my union dues all these years. We don't have a recognised union, so my union rep was external.
We initially got it postponed, because the first date was only two working days notice, and I couldn't get a rep to attend then. HR did go with our proposed changed date, which was what most suited my rep, so we met yesterday, not Monday.
Rep was very keen to be clear what the charge was, and for HR to be clear about what I had done that I shouldn't have done, and what I shouldn't have done that I should have done.
I had a prepared statement, which I read out, and sent them a copy of afterwards, so the scribe didn't have to try and keep up with what I said for the minutes. It started with a brief summary of when I started at the company, doing what, and that I had a good work history. It covered that I was not guilty of the allegation, and them went through a timeline of what I had been doing and why, and finished with me refuting the allegation again and what I hoped the outcome would be. This was about the third iteration the rep had reviewed, and in a couple of places, he had said thongs like, "if you phrase it this way, that will be helpful if it gets as far as tribunal."
After reading the statement, they asked me some questions about the case. Then we adjourned for about 25 minutes, while they decided on the outcome.
The main difference was that my outcome was no further action, as they never had a case in the first place, and it shouldn’t have got past an investigation (which had never been clear to me it was an investigation meeting - there were one or two other bits where it was pointed out they didn't follow their own process, as well.) But I hope describing the prep we did is helpful.
Also the ACAS guide to disciplinaries and grievances (can't remember the exact title) is easily googleable, and he should have a good idea of what's in that, and the employer's own disciplinary procedures.