Please correct me if I'm wrong, but you cannot any longer instruct AND BE REMUNERATED for it if you have only a PPL and FI rating.(Have recently come across an alleged case of this.) I assume that there are no 'grandfather rights' on this one.
So far as I remember, this all changed in the run-up to JAR with abolition of CPL Restricted and BCPLs. Instructors are professionals and must hold CPL/ATPL to be paid for it.