Actually, SW, it is para b. of LASORS H1.8 which applies in your case:
The holder of a valid CFS QFI category who, in
the 12 months has not completed a CFS
standardisation check (and/or been granted a
Certificate to Instruct) on single-pilot, single
engine piston powered aeroplanes, will be
required to complete training at the discretion of
the Head of Training of a FTO approved to
conduct Flight Instructor (Aeroplane) Courses,
and pass a FI(A) skill test with an authorised
examiner.
You also need to meet the pre-requisite Flight and Theoretical
Requirements outlined in LASORS H1.8.
The seminar requirement applies to those revalidating or renewing an existing FI Rating, not to initial issue.