As an aside, a friend and I once had a discussion about how anonymous cash really was.

I don’t know if the serial numbers of notes are read by the machine as they emerge from an ATM. I presume they are, but they certainly could be, if they aren’t already. Suppose that you extract 6 x £10 notes one day, and a couple of days later, four of those serial numbers are found in the wallet of a drug dealer when he’s arrested. How likely is it that they didn’t come directly from you?

Fun topic for pondering in a pub…