I thought that any smallish folding bike was allowed into the main part of a train but the other day I picked up an official train company leaflet saying no bikes can go in a carriage unless they have LESS than 20" wheel diameter, which in most cases would mean 16" as not many bikes run 18".
The leaflet seemed to be sponsored by Brompton bikes. Was there always this wheel size restriction or is it related to the leaflet sponsorship?

