Except the DDA and RVAR have now been superseded by the EU PRM TSI (Technical Specification for Interoperability for Persons with Reduced Mobility) for heavy rail, and the Rail Vehicle Accessibilty (Non Interoperable Rail System) Regulations 2010 for light rail (metro, underground and tram systems).
Both sets of regulations are linked from the D(a)fT website.
Cheers,
Barry
Incidentally, I read the other day that apparently, the whatever it's called now regulations for Buses also stipulate minimum seat spacing, which does seem a worthy idea. I do hope that this is something that will be extended to trains.