Its easy for the revenue guys little handheld machine to check a valid
oyster card or not since the data is held on the card. But how do they deal with
contactless bank cards? The card itself will have no knowledge of the journey
and I doubt these devices have a wifi connection to TfL HQ to check if the
bank account has any money in it and whether the card has been touched in etc
so how does it work? Or not?

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Spud