Miss PN2 received her letter today. It was dated 24th Jan. I guess the 11 day delay is because the post office couldn't handle half a million letters on day 1.
When Mrs PN saw the requirement to prove identity her reaction was a more volcanic reaction than some mentioned here earlier.
The only bright spot is that Miss PN2 is now Mrs xx1. However Mr xx1 is probably going to get a letter too.