How does that work then?
Passenger buys a railcard discounted ticket, we have no way of knowing they actually have a railcard. Passenger boards train, ticket gets checked and tells guard they have forgotten it so guard issues a 1-day railcard and passenger gets cheaper travel.
Then what happens? Specifically if they didn't have a railcard in the first place?
1/ Passenger buy railcard discounted ticket
2/ Passenger is checked, says she has forgotten railcard
3/ Guard checks eligibility of passengers for claimed railcard if at all possible (presence of a child 5-15 for F&F, two travellers for TT, some proof of age for 16-25 or Senior, some proof for disabled)
4/ If eligibility is blatantly wrong (only one traveller for F&F or TT, wrong age), then do whatever guards do in case of fare evasion
5/ If Eligibility is in doubt (no proof of age or disability), then issues a full fare (as now)
6/ If eligibility is in no doubt, and cost of RailCard is less than cost of full fares, then issues a 1day "railcard" at 30£ (or 20£)
7/ If eligibility is in no doubt, and cost of RailCard is more than cost of full fares, then issues full fares.
Doesn't seem very difficult to implement. Can't see obvious ways to abuse it grossly (perhaps with TT, where single passengers use mobile technology to "pair" with strangers, hmmm) . Passengers who genuinely forget their railcard have a small additional layer of protection, but that comes at a _commensurate_ cost (none of that 250£ for forgetting a 30£ card)
I am probably missing something obvious.