it's a long path,155 hours before the 35 hr commercial flying course,theoretical exams (if you can find a school,as yet i think JAR are still running ATPL(A) with helicopter add ons only) hour building to 300 hrs .then 25 hrs for instructor rating +100 ish ground school.
After all that you can look to earn 30-40 £ a flying hour.
having said all that i does seem there is demand at the moment for instructors after the glut of 2 years ago
good luck