What exactly do you want to teach?
Briefly:
If you want to teach for the multi-engine course and IR course, then you will need to become a CRI and an IRI. For the CRI, you need to have 300 hours on aeroplanes, and also 30 hours P1 on MEPs. N.b. the 30 hours must be on MEPs - other MEs (jets/turbo-props) don't count! For the IRI, you need either 800 hours IFR time, or 200 hours by sole reference to instruments.
I'm not sure how many jobs there are for people with these qualifications, because most schools that teach these courses also teach for the CPL, and would expect you to be qualified to teach for that course.
If you want to teach the CPL, then you need to do a Flying Instructor Course. You will then need to do 200 hours of instruction, including supervising 25 solo student flights. (You can get the "Supervisory Restriction removed from your instructors rating after 100 hours and 25 solo supervisions, but you need 200 hours instructing before you can teach for the CPL course.) You will also need to remove the No Applied Instrument restriction from your instructor rating to teach for the IR (200 hours IFR or 50 hours by sole reference to instruments), and add Multi-engine priviledges (500 hours on aeroplanes, including 30 hours P1 on MEP - and see my comments above re. needing to be MEP and not ME turbo-prop or jet.)
If you follow the second option, then you could earn £25-£40k (there was a recent thread about this). But you will need to do your apprenticeship teaching PPL and earning bu88er-all while you build up to 200 hours of instructing time.
Hope that helps,
FFF
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