Bob Wood ) gurgled happily, sounding much like they
were saying :

If relying on Pre-Pay, an Oystercard will never become a Travelcard.
What it does is to cap the day's spending at 50p less than the
appropriate Travelcard for the journeys made. It can never become a
Travelcard because it can never be used on most National Rail services.

An ODTC without the ability to be used on NR used to be called an LT card
and cost a chunk less than an ODTC...