Sorry Heliport I was answering the second part of Simon's question, because I can't find any reference to this CPL + CFI 'requirement'. So I thought the 'loggable' issue was moot.
AFAIK PPL instructors with grandfathered rights to charge for instruction still exist. In addition LASORS confirms that it is possible for a PPL to get an instructor rating, but since he can't charge for instruction, as Simon, says it's not clear why anyone would do that. PPL/CPL should make no difference to whether it's loggable.
While we're on the subject, can anyone confirm that the JAR to old money term mapping is as follows PIC = P1, PICUS = P1/s, and Dual = P/ut. What is SPIC (student pilot in command) then - student solo ?
Edited:
And SZ1,
AFAIK it's not legal for someone who is not qualified to operate the controls, unless they are under instruction by a qualified instructor. That should rule out both your scenarios.