How many different anonymous oyster cards will you use. Likely one card, for years? At best it's pseudonymous not anonymous - a dataset identified by a GUID

How many different anonymous oyster cards will you use. Likely one card, for years? At best it's pseudonymous not anonymous - a dataset identified by a GUID not a name. That card has a unique id, and so a large data history attached to it. Commuting habits will be evident in the data. Should the person who uses the card need to be identified, it won't be that hard to find a clear image of them using the card to enter or exit at an otherwise quiet station in that history.