Is that correct FFF that you could technically instruct CPL students on a PPL?
No, it isn't but I'm not sure that's what FFF was saying. To instruct for the PPL and to be remunerated, you must hold a CPL, which is also all you need to instruct for the CPL (plus the required experience). The basic rule is that you cannot instruct for something you do not hold yourself.
However, you do not need either an IR or a MEP - there are many CPL training providers who do not use twins and many who are not approved for the IR.
To answer the original question, the minimum qualifications to teach for the CPL are to hold a CPL and unrestricted FI rating with 500hrs total time, of which 200hrs is instructional.