Nope, no one other than the booked crew.A high profile passenger would usually involve some sort of driver manager on board the train, wouldn't it? Or maybe it doesn't in your TOC.
Depends how high profile the person is, I suppose. PMs these days are just glorified celebrities
No one else other than control knows, police get in touch with train manager but that is it, strictly need to know, and no extra resource.
Plus on some days like during this current election period, may not actually find out until on the day that someone is travelling as there plans will change frequently.