There is no such thing as a Bi-Annual or even a Biennial in Europe!
but can be checked by an instructor with less than 12 hours
There is no requirement for a check with an instructor either.
One of the revalidation requirements is 12 hours experience in the last year to include a dual flight with an instructor, this is training not testing!
If a pilot does not have the 12 hour experience requirement then he has to pass a Proficiency Check with an Examiner.
The pilot would have to convince the Head of Training of an ATO or RF that he/she was fit to take a Revalidation Flight Test
For a Revalidation Proficiency Check there is no requirement to go anywhere near an ATO; that is for Renewal!