would the caa not have a fit if this was done in practise
If we go back to about 2001 a very nice lady at the CAA (E C-H) who looked after Examiners used to advise PPL schools that this was the case. A FI can teach Ex 19 and Radio Navigation but to teach Instrument Approaches or Limited Panel you have to have the no applied IF limitation removed. Nothing has materially changed since then. An interesting JAA anomaly is that a CPL Course includes LP but, a FI who can teach on such a course has never been taught to teach LP!