Ok, so you are correct that you have very few rights in the circumstances due to your length of service.
In relation to what has happened so far this is really a non-issue I am afraid. I agree it could have been dealt with better but this is only a procedural issue and these cannot be challenged with less than 2 years service so you have to ignore them.
You will have better rights to argue that this is not gross misconduct because you did not know the exact procedure due to the lack of contract or handbook being issued to you. However, it does not mean a dismissal can be acoided, just not classify it as a gross misconduct dismissal, hence you will be entitled to notice period.
So really your only rights on challenging any of this is in relation to whether this is gross misconduct or not. If you feel like you want to leave as a result of all that has happened you can offer to resign, serve your notice period and leave, asking them to drop the investigation and disciplinary in return. Otherwise you have to continue with the process and defend yourself and challenge any gross misconduct as being too harsh, remembering the dismissal itself cannot be challenged, just its seriousness.
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