At the Midlands show I came across these people right by the entrance.

They have a website and are promoting the idea of DIY hand propelled railway vehicles.
They displayed an original wooden 3 wheeled one and a home made 4 wheeled one for narrow (2ft?). They are looking at finding parts and suppliers to enable more people to build this style.

Seems like fun and they have been arranging opportunities for people to run their own creations on real track for several years. See more on the website.