Mike
Thank you for your helpful update. My only issue is that TFL are now saying one thing and GA through their customer service team and the MD another. GA need to change the announcement on their trains passing through Tottenham Hale to “Oyster Cards can only be used beyond this station with a suitable extension”. At the moment the announcement states that you cannot under any circumstances travel beyond TH with an Oyster Card and may be prosecuted for doing so or face a penalty fare. This is why I have had so many issues with GA staff.
Regards