Well feel free to disagree with me all you like, but the fact is you won't be able to get through the ticket gates if you have a negative balance on your Oyster Card, even if you have a Travelcard. I know this through my experience of working on the gateline and also because it says so on the TfL website.Sorry but I don't agree with this one. If you have a negative payg balance and you also have a travelcard valid for the journey you wish to make,then you have a valid ticket,as you are using the travelcard. As long as your journey is wholly within your travelcard zones,to my mind any payg balance on your card is irrelevant.
For National Rail:
and for TfL:You can use a valid Travelcard season ticket on your Oyster card provided that, where using a station with ticket gates, any pay as you go balance on your Oyster card is not in debit. Should the pay as you go balance on your Oyster card be in debit, you will need to clear the debit before you can use your Travelcard through the ticket gates.
You can use the Travelcard season ticket on your Oyster card provided it is available and valid at the time you travel and any pay as you go balance on your Oyster card is not in debit. Should any pay as you go balance on your Oyster card be in debit, you must clear the debit before you use your Travelcard season ticket.
I don't understand why you don't need a photocard with a Travelcard on Oyster, given they would be quite easy to check, strange they abolished the requirement.Several of tfl's policies need to be looked at as again,to my mind,they are unenforceable. For instance,you can lend your Oyster card to someone else to use if it contains payg credit,but not if it contains a travelcard. How can they enforce this? If I had a Oyster travelcard season and I lent it to,say,my brother and he made a journey with it,as long as the journey was carried out correctly how could tfl prove it wasn't his card?
I wouldn't say it's totally unenforceable, especially in the case of a Mr. using a ticket registered to a Mrs., or if there was some investigation going on, but it could be used against one using a stolen ticket.