An OEP is needed when a card holder has both a Travelcard season
ticket and Pay-as-you-Go credit on their Oyster card and wishes to
travel from a station within the validity of their Travelcard season
ticket to a station within the Travelcard zones but not within the
validity of their Travelcard season ticket.

Not for travel on the tube, surely? I thought you always used to just
touch in and out and it automatically charged you the correct fare? Or
has that changed?

So presumably the above only applies to journeys on National Rail?

What about journeys part on the tube and part on National Rail? What
about London Overground?

Assuming that the above quote is an oversimplification, where is the
actual rule stated?

If the journey is made without an OEP, and the card holder touches in
and out, then the correct fare is charged.

Right, that's the whole point of smartcard ticketing. So that's just
like it's always been, then?

In all these cases, the holder is liable to a
Penalty Fare if challenged when outside the validity of the season
ticket.

Hang on, have I misread that, or is someone seriously saying that you
can now be issued with a penalty fare for paying the *correct* fare for
the journey.

Despite this, London Travelwatch have received a
complaint where a passenger with a Zone 1-6 Travelcard season ticket
on their Oyster card failed to touch in when travelling within these
zones and received a Penalty Fare.

Under what circumstances would a Zone 1-6 Travelcard *not* be valid
within Zones 1-6? Now I'm really confused.

How are customers supposed to understand any of this? I'm now quite
thoroughly confused...

-roy