Not sure I agree with Jarvey! Before commencing an FI course (Fixed Wing Single Engine Land) you will need 100hrs P1 with a CPL or 150hrs P1 without a CPL.
Unless you want to be paid you do not need to have a CPL or the CPL knowledge exams. If you do want to be paid then you need to be issued with a CPL be this via the CPL or ATPL route. But you need to license not just the written exams.
You might also want to read this:
http://www.pprune.org/forums/showthr...Instructor+IMC
You should also read the revelant bits of the licensing regulations here:
http://www.caa.co.uk/docs/33/LASORS.PDF
BTW, I'm training at the grand old age of 37!