One of the pre-requisites is the ability to look things up in obvious places such as LASORS, since any prospective instructors must expect students to ask them questions and must know where to find the answers.
If you were to acquire this skill and look in LASORS, you would find that before starting the course you must have 200 hours total time on aeroplanes, of which 100 must be P1 if you hold a CPL. (If you don't hold a CPL, 150 hours must be P1, and you must have completed the CPL or ATPL written exams.) There are a number of other smaller requirements, after which you take a flight test, and if you pass the flight test you can start the course.
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