From the AIS NOTAM page:
AGA : FROM 05/04/26 16:07 TO 05/09/26 12:00 EST U0488/05
E)THE ONLY INDENTIFICATION ACCEPTED FOR CIVIL CREW AND PASSENGERS TO
GAIN ENTRY TO RAF NORTHOLT WILL BE:
INTERNAL FLIGHTS, A UK PHOTO DRIVING LICENCE OR VALID PASSPORT.
INTERNATIONAL FLIGHTS, A VALID PASSPORT.
FAILURE TO COMPLY WILL RESULT IN PERSONNEL BEING DENIED ACCESS.
think that covers this instance.
PM