Greg,
You seem to need to see it spelled out rather taking the word of people who know.
So here you go:
From FAQ number 1, chick on ticket types, after those accepted it shows those not accepted
SORRY! The following tickets are NOT valid for 2FOR1 offers:
Oyster Cards
TfL Issued Travelcards
Freedom Passes
Heathrow Express & Heathrow Connect Tickets
Stansted/Gatwick Express in-flight (or mobile) tickets where
the National Rail logo is not present
BritRail Passes
EuroStar Tickets
'The London Pass'
Digital Tickets - where the National Rail logo is not present
MegaTrain Tickets
Note carefully the 4th line there.
Also note FAQ number 2:
What days will my train tickets be valid to claim the offers?
Single
tickets - These are valid only on the day of validity. A days
Travelcard must be purchased from a train station and feature the
National Rail Logo.
Return Train Tickets - You will be able to use
your return train tickets with the vouchers at any time between the
outward and return journey - if you came on Thursday and returned on
Sunday, you could use the vouchers on Thursday, Friday, Saturday &
Sunday. In order to do this please ensure that you retain the outward
portion of your ticket as you will need to show both tickets at the
attraction - just ask the staff at the ticket barrier to let you
through which they will be happy to do.
A return ticket is one issued for out and return between the same points, issued at the same time with the same ticket number on both parts. A return ticket is not a cobbled together group of singles. The return ticket will have the legend OUT on the upper right corner of the out ticket and RTN in the same place of the return. A single ticket will have SGL written there.
Your final comment above:-
It may be we just try and see what happens at the venue in question. (Tourists you know). Always nice to know how firm a footing i'm on when I do such things tho.
is troubling to me. As somebody who deals with chancers and fare dodgers every day that is exactly the attitude I would expect from one of them.
You know it is wrong but you figure that if nobody catches you then you are safe. I bet you cheat on other things too.
If you don't want to follow the rules and laws don't come.