You have it correct (Customs should notifiy the Border Agency).
However if you read the GAR instructions it says:
Quote:
All flights notified for Customs & Immigration purposes should be sent to:
NCU (National Co-Ordination Unit) – Fax 01708 862521 (overseas; +44 1708 862521) or 0870 240 3738; email
[email protected] (please put GAR, registration and airfield in the subject of the email)
(Some local offices may still require separate notification in addition to the above)
"Some local offices" in this context can only mean some local Customs offices, as it is HMRC that is giving the instructions.
If I send an email to the National Co-Ordination Office, I expect them to co-ordinate and I don't ask if I need to inform anybody else. All I do is keep a copy of the email.
I depart from and return to one of the "Other Airfields", and have yet to meet a Customs or Border Agency officer.