HMRC are at it
HMRC sent me a dead tree letter saying I had to file a tax return for two years ago. A year when I earned no money, not a bean. I sat on the phone and eventually got to talk to a nice young man who apologised told me to ignore it and shred it. Their systems apparently will do this with only minor provocation.
In my case it seems to be registering for self employment because I am trying to earn pin money by tutoring in Biology and general Science. It's unleashed all sorts of havoc at HMRC which makes you wonder how competent their systems really aren't.