That map is from about 1850.
Major rebuild around 1903 and many later changes.
Suggest searching nls for a large scale map of the era you wish to model.
That plan is not entirely faithfull to reality. There was (and stiil is) a trailing crossover to allow departures from platform 6 to the Up Main. There never was AFAIK a facing crossover Down Main/Up main just east of the platforms. Fisherton Yard never had a direct connection to/from the running lines - it was connected to the stub end of the GWR Down line which was a kickback from platform 1; just as the present day Traction Depot is connected. Several other changes possible depending on your space/desires.
There was previous legislation which I believe was superceded by the 2011 act. IIRC legislation was introduced soon after WW2.
As well as various safeguards to protect young fingers etc it also limited the maximum voltage for powered toys to 24v. Previously , I think, there had been 110v locos!
Agreed.
To clarify:
you wrote - "there is no reason why other railway companies should do the same."
whereas I think that you meant to write - there is no reason why other railway companies should NOT do the same.