I don’t understand this. The UK does not have a “port of entry” system. You can land at any aerodrome, subject to having filed the GAR on 4hrs PN for inbound from EU or 24hrs in/out non-EU.
And yes exactly the GAR should not go anywhere near to aerodrome. The personal data on it is not their business and in any case they should not be handling this data within the provisions of GDPR or whatever.
Yes from France, GAR directly to UKBF with 4h PNR will do, it should not be an airport buisness or even worth correct or wrong entries in the AIP (but some airports think the flight needs a “special approval” or “clearance” from them some obscure or legacy designations or under their agreement, or just list a worst case 24H, Cambridge is PPR 24H though but nothing to do with GAR)
I am 100% sure flying from Germany to LaRochelle, no PPR/PNR will be a non-event !
I remember being asked for a copy of the GAR confirmation by a british handler. I just transfered the onlineGar email so all our personal data was in it 
I should just have given the GAR confirmation number.
