> Oyster payment cards are virtually impossible to use anonymously
You can just buy them with cash from the machines, right? Isn’t it a rare example of a public service in the UK that does not involve a bunch of surveillance?
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.