THTF is about right. I've not got my JARFCL handy either but one central pillar of it is that you must always hold the rating for which you are teaching. So you must be ME rated to teach ME, have an IR to teach IR etc. As far as previous experience goes, it's not quite as bad as THTF says. You need 30 hrs P1 ME but only 10 hrs in the last 12 months (still expensive to get). The ME instructors course is about 6 hrs in the air but quite a bit of ground work. Finally you need a test with an FIE.