About an hour and a half after landing Fairoaks, I received a mobile call from the Distress/121.5 cell at Swanick asking if I was ok, as Cambridge had called them due my overdue /non-arrival there.
I assumed that an IFR plan would be closed on landing, but it seems if you divert your original destination is not advised by the ATC system.
It's up to the ATS at the aerodrome you land at (or you, if there isn't one!) to send an ARRival message, telling the interested parties that you've arrived safely at a different airport than planned. Sometimes, they don't know, or forget, that it's a diversion. Better to prompt them.