No action needed by the authorities
On the contrary, even the DfT could intervene on the basis that franchise operators must adhere to the TSA which does not provide for an option of denying the passenger the service to which they are entitled:
14 DISPATCH OF TICKETS
(1) Minimum Standard
The Operator will determine its own Ticket delivery arrangements which must be clearly explained to Purchasers before or at the time of purchase. The minimum Standard is that Tickets being despatched to destinations in the United Kingdom will be sent to Purchasers by First Class Post or other equivalent method.
(3) Arrangements to apply when Tickets dispatched by post are not received by the Purchaser
Where a Ticket has been despatched to the Purchaser by post, and does not arrive by the time specified when the transaction was completed, the Operator must advise the Purchaser to contact the Site through which the Ticket was purchased to establish how to obtain the Ticket for the journey purchased.