I agree with David’s advice.
However, I would also query what has changed. Have you only just disclosed MS, despite being diagnosed six years ago, and they have panicked?
If they have known from the start, why did they let you take this job, and do it for a year, before deciding it was a problem? Has there been a recent change of policy? Or has somebody perhaps raised concerns about you, because you seemed tired or otherwise unwell?
I do get the impression it’s bureaucracy, and perhaps a fear of legal action, that’s behind it, rather than willful discrimination, but I do agree you should have some input into what is still OK for you to do.
If you were driving, I can understand they might worry about whether you would still be covered on the company insurance, and whether they might be held liable if you had or caused an accident whilst at the wheel, and it emerged they had not taken any precautions to protect you from becoming over-tired. I’m not saying I would necessarily agree with it, even then (people with MS are allowed to drive), but they could argue it was not a risk they were comfortable with.
But I don’t see how you are endangering yourself or anybody else - even hypothetically - just by sitting on a train.
I admit, I think I would find such a job too much now. I haven’t worked in over two years (not exclusively health related - was made redundant anyway, and realised I wasn’t sorry). But in my old job, it did occasionally (much less often than fortnightly) happen that I was required to go on long train journeys for training, client meetings or whatever, and occasionally to stop away overnight. I was beginning to find this pallaver difficult, and to try to avoid it - not putting myself forward for training, and opting to do meetings by conference call wherever possible - that sort of thing.
But that certainly doesn’t mean nobody with MS is able to do it, and even had I continued, I’m not sure it would have posed any tangible risk. I just would have found work a harder slog than necessary, so I suppose my overall welfare would have been affected, but no direct proof my health would have been - i.e. that business travel causes relapses or progression!
We did have an agreement that if I did go away, I must have pre-booked train tickets to be sure of getting a seat, and I must be allowed to leave on time to catch the train that was booked - no meeting overruns, and ending up having to stand all the way from Reading to Bristol (about an hour). It was also agreed that I did not have to take my laptop with me to offsite meetings, as would usually be expected of someone in my position, because it was a lot extra to carry (it was a real old-fashioned brick of a thing, much heavier than the new models out today).
So there were certain compromises, but they did not go as far as saying I wasn’t allowed to go.
I do remember, when I was first diagnosed, one of the first things they asked was: “Could it have been anything we did?”, so they’re extremely paranoid about anything like that. I didn’t work for the Civil Service, but in what I would-describe as a Civil-Service-like environment - i.e. close ties with government departments, and former nationalised industries, and that sort of thing.