From personal experience, if you use an EMV card that has been blocked on TfL services, you will sometimes be able to travel. I did this by accident once. I cou

From personal experience, if you use an EMV card that has been blocked on TfL services, you will sometimes be able to travel. I did this by accident once. I could see TfL repeatedly trying to debit my account with incorrect information for about a week. I doubt all of their readers are offline, and I suspect that a card gets blacklisted if it declines. I suspect this is also because they only charge at the end of the day once they have computed the correct fare (with capping etc)