Mr T,
You'll need to take (and pass) the JAR CPL or ATPL theory exams and then take (and pass)a FI course. You'll also need a total of 200hrs flight time with 150hrs P1 before you can start the FI course as a PPL (reduced to 100Hrs if you take/pass a CPL course and skills test before the FI course).
Four Forces aviation are currently running JAR CPL theory courses and ATPL theory courses can be found at a number of training establishments, often discussed on this forum.
Another route for you (??) might be to wait for an instructors rating for the new NPPL. This won't start till later this year (?) and you won't be able to teach JAR PPL students. Current proposals, still under discussion are for a minimum of 200hrs P1 plus a training course/test for the NPPL FI rating. Discussions are taking place I believe about how these instructors can be paid (without holding a CPL)...
I'm currently taking doing a JAR CPL course with a view to doing a FI rating and CPL skills test. You can be sure, with my luck, they'll bring out the (far easier/quicker?) NPPL FI rating just as I finish my courses, agghh....!