I re-sent my query to my local FLO on the Langham Hall rally, and got this:
Thank you for your email. I will be working across the county and therefore out of the office until Wednesday 29th October. I will have limited access to emails during this time, however please rest assured that your email has been received and will be addressed as soon as possible. If you have an urgent finds related issue or Treasure declaration please contact the Portable Antiquities Scheme Treasure Department on +44 [....]While I am resting assured that if I were a metal detectorist I'd now get a reply, I really wonder whether the FLO has a mobile phone for use when "the other side of" an English county, and why Treasure declarations are not being directed to the Coroner, as the Treasure Act requires.