Some people on this thread may already be aware but it's worth pointing out that if you have a hearing aid you qualify for a disabled person's rail card, giving savings for you *and* one companion of 1/3rd off your tickets.
That seems a bit of a strange loophole, as many hearing problems not correctable with aids do not qualify and vision problems correctable by glasses do not qualify. .
The eligibility criteria is "Are registered as deaf or use a hearing aid”. A Hearing Aid prescription (or NHS battery book) is one of the ways you can demonstrate eligibility. There are others.