Interesting. I had assumed it was carried across from the NRCoC but apparently it was not.Where is that written ? It is not in the NRCoT.
The NRCoC stated (my bold):
A ticket that has been issued to you is evidence of a contract between you and each Train Company whose trains you have the right to use. Where the company selling you the ticket is not one of the Train Companies on whose services you are travelling, the seller is acting as agent for the Train Company or Companies in whose trains you are entitled to travel.
If a ticket entitles you to any goods or services from another party (including the right to travel in another party’s transport services), it is also evidence of a contract between you and that other party. The conditions relating to these additional goods or services may be different, and will be obtainable from that other party.
Tickets remain the property of the relevant Train Company. Each ticket is issued subject to:
(a) these Conditions;
(b) the applicable Byelaws;
(c) the conditions which apply to Electronic Tickets, Smartcards, other devices used for storing Electronic Tickets and certain types of reduced and discounted fare tickets as set out in the notices and other publications issued by the Train Companies whose trains you are entitled to use; and
(d) the conditions set out in the notices and other publications issued by another person if the ticket enables you to use any of their goods or services. Train Companies will ensure that you can be provided with or have access to the conditions applying to any ticket you buy, as well as the Byelaws, before you buy your ticket.
In the case of electronic tickets and tickets issued on Oyster cards, see Condition 9.
What's interesting is that the NRCoT doesn't actually say that your ticket is evidence of a contract:
Your Ticket is evidence of your entitlement to travel on the National Rail Network, as allowed by the type of Ticket you have purchased. It is your responsibility to keep it safe and it should be looked after with care