@cstross I work with disabled students and I've tried (and often failed) to get trip-leaders to give clear advance info and consider ways to adjust things.
One occasion, despite extensive discussions about distance/terrain in advance, a disabled student of mine was left sat for 3 hours on their own sat on a rock cos the terrain was not as described & therefore inaccessible. We'd have hired a specialist wheelchair or done a different thing IF the leader hadn't lied to me/student.