Graham J wrote:
* You do need to touch-in on Tramlink if you have a season ticket
_if_
(and only if) you're travelling to Wimbledon, otherwise the
automatic
gates that also serve the NR and Tube platforms get confused and
will
charge you for a tube journey.

AFAIAA the situation is actually that the gates will refuse to let
you out
at all and it is a deliberate anti-fraud measure. The reasoning being
that
passengers could arrive on National Rail trains from far off
destinations
without any ticket, or with the lowest price ticket that could have
allowed
them to board the train at their origin station, and then have an
Oyster
card with just a bus pass on it to allow them to exit. By forcing
all
Tramlink users to touch in it means that bus passes will only open
the gates
if the passenger arrived at the station on Tramlink.

Although it's simple enough for such passengers to hop on a tram to
Dundonald Road, touch in, and be back in a couple of minutes and
straight through the barriers. Isolating Tramlink at Wimbledon with
another set of barriers (if physically possible) would prevent this if
it was thought worthwhile - I think - at the expense of making it
horrendously complicated for your poor Oysterite.