Peculiarities of certain locations are pretty standard stuff, the overall Rulebook still applies but with 'local instructions' for those places where certain procedures are necessary. The Severn Tunnel is a good example, there are numerous others nationwide. Was the '38 stock ever modified to include door egress equipment, or does it retain the standard Underground layout of emergency escape via the cabs? If that's the case, it's a pretty easy situation to control; a crew member at each end and your pax are contained. I can't imagine many would attempt a swift exit whilst sat on Ryde Pier anyway somehow!
There are also a multitude of TOC-specific rules these days, SWR no doubt have an 'appendix to the Rulebook' and no doubt it includes instructions about not crossing the open gangway between '38 stock cars, and so on.
As for the infrastructure, I very much doubt NR would harbour any remote desire to have it back!