When considering the legitimacy or scope of the Railway Byelaws (which seems to have become a current theme in this wandering thread) it might be worth remembering that these Byelaws are intended to regulate the activity of persons while on Railway property, for which purposes, the Railways are private property.
In this light, comparisons with a motorist speeding on the public highways are unhelpful; better comparisons might arise with the regulations (which include Byelaws) that apply to persons on other private property (e.g. heritage houses, care homes, prisons, schools, ports and hospitals).
Other, more comparable, Regulations apply to the workplace (where the public may be admitted). These have been created by similar delegated legislation and include the Management of Health and Safety at Work and Control of Asbestos at Work, and some regulations on Taxation. These have all had the effect, at some time or other, of rendering an 'innocent' person or enterprise in a technical 'breach' of the regulations overnight; despite vigourous and articulate protestations. There's also the famous example of the novellist Ian McEwan being investigated for a Byelaw breach after admitting taking pebbles from the protected Chesil Beach during a radio interview.
My point is, that the Railways are as entitled to create Byelaws to regulate persons on their property as are many other bodies. That authority has been already been challenged. Unsuccessfully, in Boddington v British Transport Police. To imagine that the Railway Byelaws might now be considered ultra vires in a Judicial Review after so many decades stretches my credulity.