whos2091 wrote:

It varies but they often do. Keep your paper portion handy - though
they don't actively ask to see it if the specific guard has no oyster
reader, it saves having to queue up behind one that does.

Seems like that practice opens the door to a good deal of fare evasion.
(Person A buys an Oyster-based Travelcard and gives or sells the paper
portion to person B. Now A and B can travel on the same card at the
same time!)
--
David of Broadway
New York, NY, USA