Sandy Wings, if you are flying for the airlines, you will hold either an ATPL or a CPL with ATPL knowledge, upgradeable to ATPL once you have 500 hours co-pilot time.
You did NOT need to 'renew' your PPL, you needed to renew the SEP Class Rating which you should have had included on your Professional Licence.
You do NOT normally need to attend a FI seminar for initial issue of a FI rating, unless your QFI Category had lapsed.
The requirements for military QSPs are clearly spelled out in LASORS H1.8:
H1.8 MILITARY CONCESSIONS FOR ISSUE
OF A FI(A)
Credit is available only to holders of a CFS QFI
category. The holder of any other military instructor
qualification will not qualify for any credit against the
FI(A) rating requirements.
a. The following terms are for holders of a valid CFS
QFI category who has completed a CFS
standardisation check (with a CFS Agent, and
been granted a Certificate to Instruct) on
single-pilot, single engine piston powered
aeroplanes, within the 12 months preceding the
date of receipt of the FI(A) application. The
holder of a valid CFS QFI category who does not
meet this requirement should refer to paragraph
(b) of this section. The holder of a non-valid CFS
QFI category, including ex-QSPs, should refer to
paragraph (c).
b. 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.
c. The holder of a lapsed QFI category including ex
QSPs will be required to apply to PLD for an
assessment.
There are further pre-requisite flight and theoretical requirements which must also be met; these are again spelled out in LASORS H1.8.
Basically, if you want to instruct on civil light aeroplanes, you need to start on this within the 12 month window of your last CFS Standards check. Otherwise you throw yourself at the mercy of PLD.
And yes, the CAA certainly DO try to make it easy-but they assume that you can be ar$ed to do the necessary research first! Being rude about them because you cannot assemble excreta and hosiery correctly is hardly fair. Quite a lot of work has been done with the CAA on securing credit for military experience; sometimes I wonder why anyone bothers, if that's all the thanks they get.