3.6 Tickets routed via stations that are not on a permitted route
Occasionally, tickets will be routed via a particular station that is not on a permitted route for the through journey.
In this case, permitted routes are defined as from the origin to the via point, and from via point to the destination. This was confirmed by ATOC when a customer enquired about a Sheffield to Blackburn ticket routed via Burnley.
Originally Posted by ATOC
The Routeing Guide lists the permitted routes for a particular flow. The actual routes that the customer can use, is sometimes limited by the route shown on the ticket, which may stipulate that the journey must go via a particular location. In some cases however, the opposite applies and the particular “via” location is outside the range of the usual permitted routes and travel via that location would not normally have been permitted. But because a flow specifically routed via that location has been priced by the Train Company , travel is permitted via that location. It appears that this is the case for Sheffield – Blackburn, via Burnley.
In this instance you are correct and you should look up the permitted routes for Sheffield-Burnley and Burnley-Blackburn.