Think Plymouth Powerboat School run Instructor Courses as well.
Check the RYA website www.rya.org.uk
and follow the links from working with us.
Also one in Exemouth www.quaymarinetraining
the new Powerboat Instructors Handbook G19 is out very useful reading prior to the course and come April there will be a pre course assessment so may be worth your while re doing your level 2 or getting some practice on the water go through the direct entry assessment in your log book and see how you do.
Your Knowledge of theory needs to be good also above what is required for level 2 more Day Skipper.
Good luck with it .