In message .com, MIG
writes

SamB wrote:
They shouldn't need to read your Oyster - it's of no consequence to
*them* whether or not you have the travelcard on your Oyster, so they
should just sell you the ticket, and then if you don't have the
travelcard you would get done by a ticket inspector. Wherever you go to
buy the extension (anywhere is fine), just ask for a Boundary Zone 2 to
Balham return.



They don't seem to insist on seeing your travelcard when you buy
extension tickets now, presumably because of Oyster, but they always
used to.

I've certainly had my Oyster ticket insisted on being inspected when
buying extensions. Not that it has helped much - generally the NR ticket
office people (both within and without London) look confused! Inevitably
I explain in words of one syllable what an Oyster card is. I don't
actually get this problem at NR station where they also sell
oystercards, presumably because the staff are more familiar with them.

--
Paul G
Typing from Barking