Oh dear. You've been given well founded, knowledgeable advice, by a number of people who know exactly what they're talking about. You have admitted that you intentionally bought one Standard class and one First class ticket, hoping that one of you would get away with travelling in First without paying for it. Had you not been challenged, who would you have 'asked for permission'? In the eyes of the Prosecutions Department, very probably nobody. There are no grounds at all for assuming that anybody would have granted you permission to travel in First with a Standard ticket, and the idea that you fully intended to move and sit separately for the entire journey if not, or that you would happily waste the freshly bought First ticket by both sitting in Standard, is frankly rather odd.
I have to wonder if you displayed a similar attitude when caught by the revenue inspector as you have towards the contributors on here whose advice you didn't like? That won't have helped. Incidentally, have you apologised to them, particularly as they continue to assist you?
Many who are caught fare dodging fall into the trap of thinking it won't be a big deal. Most appreciate fairly swiftly that, actually, it can be, but a small minority plough on in denial. I would strongly suggest that you engage a solicitor, whose advice you might be more open to accepting and acting on accordingly.