Paul Corfield wrote to uk.transport.london on Wed, 8 Sep 2004:

On Wed, 8 Sep 2004 13:25:44 +0100, Annabel Smyth
wrote:

I have a rather similar question. Yesterday my daughter left here en
route to Tottenham Hale and the Stansted Express - all, apparently, went
well and she arrived safely.

I briefly considered accompanying her as far as Tottenham Hale, but I
wondered what Oyster would have thought - and charged me - for a journey
that appeared to start and end at Brixton Underground station, assuming
that I had not gone through the barriers at TH. A ODTC wouldn't have
had this problem, of course....

but if you were seeing her off you would have exited through the LU
gates anyway? I expect that your Oyster would have been rejected when
attempting to exit at Brixton in much the same way as if you had tried
to do so on a single ticket to Tottenham Hale when the ticket would only
have an entry at Brixton coded on to it.

Yes, it probably would, which is why I didn't do it! Had I still had a
zones 1-3 Travelcard, instead of a Bus Pass and Pre-Pay on my Oyster, I
probably would have (and maybe exited the LU gates at TH, maybe not!).
Thanks for confirming my suspicions.
--
"Mrs Redboots"
http://www.amsmyth.demon.co.uk/