The main prob is that remunerated flying instruction is Aerial Work, for which the a/c needs to be maintained to Public Transport Standards, which a PFA aircraft cannot be.
The requirement for training to be carried out from a licensed a/d referrred to in the PFA "advice" is diddly squat to do with the aircraft, it applies to all ab-initio training in what used to be called Group A (now SEP). I'd also be wary of the advice because it is dated May 2005 whereas the current ANO came into force in August 2005 and Art 126 was amended in October 2005
The
ANO
Art 126 covers the requirement for the a/d to be licensed.
Art 11 (4)
(4) With the permission of the CAA, an aircraft flying in accordance with a national permit to fly may fly for the purpose of aerial work which consists of the giving of instruction in flying or the conduct of flying tests, subject to the aircraft being owned or operated under arrangements entered into by a flying club of which the person giving the instruction or conducting the test and the person receiving the instruction or undergoing the test are both members.
I haven't turned up anything that would prevent un-remunerated flying training in a PFA type (i.e. not aerial work).