"AndreaC" wrote:

I usually use the Picadilly line from Hounslow Central but on the days
when I can't be bothered to walk the extra distance to the tube station
I get on the train to Waterloo instead. I was under the impression that
Oyster isn't valid on South West Trains and because of this mixing of
my journeys I've only used my Oyster for PAYG so far.

However, I am confused by a recorded message that I heard at Hounslow
mainline station on Friday that said something like *- 'please note
that Oyster pay as you go is not valid on any service from this
station' -* thereby implying that an Oyster with a travelcard on it is
valid.

Is that the case?

Yes

Oyster period travelcards (7 days or more) are valid on National Rail
services within the appropriate zones.

If so, how would anyone know if you've got a t/c or payg as there are
no barriers or touch in/out pads at Waterloo or Hounslow and lastly, if
an Oyster t/c is valid and I put one on my card, which zone would
Hounslow mainline station be in (given that 2 of the 3 LU stations are
in Z4 and the other is in Z5)

Hounslow rail station is zone 5.

SWT revenue protection staff have hand-held readers to check what you have
loaded on your Oyster - my Oyster has been checked in this fashion at
Waterloo several times.

Chris