Announced today- from a date to be confirmed in the 2nd half of 2026- you will need to have a National Railcard before you can buy railcard discounted fares (rather than buy such fares before having the railcard).
When buying online the railcard number will need to be registered with the relevant website, at machines the number will have to be entered at every purchase.
This is to help to combat fare evasion.
Date and further details to be advised in due course.