There has been discussion in the Postbag of the last two issues of ME & W on this topic.
Some bemoaning the lack of proper standards, and others complaining of the variation s between designers. Well, the SMEE published their standard for tracks and wheel profiles back in 1976. I don’t know if they have updated it since but in 1988a meeting was convened in Guildford to discuss the problem of different European standards in various countries. I don’t know who the British representative was but I guess that the SMEE would have been involved. Anyway, after two years of discussions a couple of common standard were published as European Standards for garden steam railways:
NEDG 311 01 / 1991 Wheel Profiles
NEDG 310 01 / 1991 Axles and wheels, Rails and points
I have a copy of those but they may have been updated since.
Russell