Make sure you have all your mitigating information down in writing set out clearly. I'd probably advise you to go to the meeting with copies of that and ensure everyone present has a copy, and ask that it be put on the official record of the meeting.
Don't be drawn into any kind of argument or discussion. Listen to what is said, make notes of it all, put across all the points you wish to make about why what they are doing is unreasonable and leave it there. Don't enter into any negotiation at all. Let them dig themselves into a hole.
If this is a procedure whereby you could be given an official written or verbal warning under the disciplinary procedure, there are steps they must follow
They must write to you explaining what the problem is, and invite you to a meeting, which they have done.
They must ensure you have been given the right to be accompanied by either a trade union rep or a colleague.
They must give you the right to appeal the decision.
If they don't follow any of these steps or anything else in their own procedures, make sure that goes on the record as well.
It sounds to me as though you may have a strong case for constructive dismissal. To claim this you would have to put in a grievance first, which I've already advised you to do. You could mention that you feel you have a case for contructive dismissal in the grievance.
I am normally on here advising people not to go down that route as it is notoriously tricky, difficult to prove and stressful.
However in your instance they've already been waving a compromise agreement about and the facts as you've given them to me are fairly damning so it's highly unlikely you'd end up in that scenario, but you could have a case and that will help you get a good settlement.