The privilege does not extend to instructing or examining candidates with higher level licences.
Not
entirely true. The CAA have clarified that a PPL/FI could instruct a CPL holder for an MEP Class Rating, conduct a SEP Class Rating training flight for an ATPL holder etc etc.
But a PPL/FI holder may not instruct for the
issue of a CPL or ATPL.
An instructor must hold the licence or rating for which instruction is being given. Hence the idea that a PPL/FI could not, for example, conduct any refresher training for a CPL holder with SEP Class Rating is
incorrect.