Would anyone be able to tell me what prevents a "Greater Anglia Only" anytime day return from London to Cambridge (as shown on brfares.com) from being offered by sites such as nre.co.uk* for itineraries involving TfL Rail services? London-Stratford-Tottenham Hale-Stansted-Cambridge is a valid route for an "any permitted" ticket. There are no restrictions in the fare data for the route code (00020) or the ticket code (SDR). The routeing guide data says a journey with that route code must include Greater Anglia, and must not include a list of other TOCs. It doesn't mention TfL Rail, which I assume means you are allowed to use them. Is there some additional information ticket sites use to work out which trains are valid with a ticket like this one? Or have I misunderstood how they use the data? * You may need to delete any nationalrail.co.uk cookies you have for this link to open correctly.