I dont know the requirements in England,but i am about to finish my CFI up over here in the US. The requirements are as follows: A commercial pilot's lisence (you have to have 250 total hours to get that), 2nd class medical certificate..and you have to take the Fundamentals of instructing written exam, Certified flight instructor written exam..then go to the FAA district office and take the oral exam and a flight check with them. I hope this helps. It's a long road, but worth it.
Chicks dig winglets.