I have to say Horizon22 I disagree with almost all that you have written above.Again (for the 3rd time), I go from my own experience whereby I have seen colleagues in the same position and they have been summarily dismissed. And that is not something you want on your record for potentially years to come.
I have seen and heard of plenty cases whereby a good Union rep will actually advise resigning because it is cut and dry that the alleged offence a) took place and b) is clearly defined in the company's code of conduct. It is quite possible that the OP is in this unfortunate situation. You don't need to be a "legal adviser" to recommend this. I have also been in disciplinary situations and won, but the facts were much more poorly ill-defined and my case was much much stronger. Why would a resignation "backfire spectacularly"? I agree that if it is believed that the gross misconduct charge is severely overtrumped you'd have lost your job when you might have just got a warning, but the Union rep evidently doesn't think it is.
If he wants to fight it, by all means ask for an adjournment and it is right they have the time to collate all the information & facts. But it is a gamble to take when the company clearly has evidence of wrong-doing. The only mitigating factor is the breakdown in the relationship, but sadly I don't think that would be enough to persuade a senior manager without strong evidence as @MotCO mentions. I'm all for wishing colleagues well but there's no point just blindly wishing "good luck" when the OP is very, very close to losing their job and that reality needs to be faced head-on.
This is by no means cut and dry. Just because you have seen others dismissed for GM doesn’t mean that it will happen in this case. All circumstances are unique. The Union has failed here spectacularly. The resignation theory backfires spectacularly when the OP walks out of the disciplinary with a final warning and suspension of travel privileges.
Being dismissed for GM will not stop a future career in any industry (remember redundancy is a form of dismissal) unless it’s for assault or possibly theft and the negative theme from some posters on this thread of ‘resign resign resign’ does not take into account the OP’s situation where resignation means no social security benefits, mortgage insurance policy support etc. It could be years before a suitable position comes up in the rail industry that the OP could apply for following a resignation.
The OP needs help and support, not someone saying Jack it in, walk away and start again If you can. Then there is the risk of the reference saying ‘resignation on day of disciplinary hearing.....’
You need to look at the bigger picture, it ain’t over ‘til it’s over and even if this does lead to dismissal, there is potential come back via an ET, appeal or settlement agreement.
But please don’t tell someone to resign their career and face possible destitution.