I was a driving instructor! I also had the advantage of being female and lots of work came my way because of this. However, I did not earn a lot of money from this. I started with a driving school and the franchise that I had to pay them was astronomical. Setting up on your own can be daunting as most pupils come from recommendations and you need a good name.DO NOT GO TO the school of motoring which is the best known in the UK , obviously I can't say the name of it.
If you are serious about going on to be an ADI try working for a small school with a small franchise until you have made a name for yourself.