Coltster
If you want 'almost' guaranteed job at the end, look to the reputation of the school. I am doing my FI(R) course with my employer, and they are good although I have not discussed their employment record, as of course I will continue to instruct groundschool as a primary job. However another local school (where a friend instructs) of similar quality in this area finds many of their graduates get work because previous graduates have impressed employers. There are schools out there giving poor training to instructors, so a good school gets known!
I don't know which are the good schools, apart from the two at Bournemouth, so you will have to investigate for yourself. Best of luck!