But does the FE has to have done the examiner briefing issued by the UK CAA?
The Examiner must now comply with the relevant entry in the
EASA Examiner Differences Document
I think the word the OP is looking for is BIENNIAL, which means every two years.
There is no BIENNIAL or BIANNUAL requirement! If revalidating a SEP/TMG Class rating by experience:
(ii) within the 12 months preceding the expiry date of the rating, complete 12 hours of flight time in the relevant class, including:
— 6 hours as PIC,
— 12 take-offs and 12 landings, and
— a training flight of at least 1 hour with a flight instructor (FI) or a class rating instructor (CRI). Applicants shall be exempted from this flight if they have passed a class or type rating proficiency check or skill test in any other class or type of aeroplane
It could be almost 36 months between such flights if it was at the beginning of the last 12 months in the first case and the end of it in the second! The CAA has also published differences to the above.