You can certainly instruct on a JAR/FCL PPL but NOT for remuneration.
It is difficult to establish how you could be paid, but if, for example, you were reimbursed for the fuel you usd to drive in, that would be OK. But nothing for flying. How the School charges the student is nihil ad rem; but you would have to be reimbursed whenever you came in rather than only on those days you flew - otherwise there would be clear linkage between your reimbursement and your flying which would be illegal.
You only need a JAR Class 2 medical for unremunerated FI work on a JAR/FCL PPL, by the way. But you still have to have ALL the 'commercial' knowledge and do precisely the same FIC as a CPL holder.
[ 18 July 2001: Message edited by: BEagle ]