The biggest hurdle is clearly becoming an aDI (approved driving instructor) which takes three exams and probably about 12-18 months preparation. Once qualified, you're realistically looking at a salary of around £20-25k per year after deducting expenses such as fuel and franchise payments. Most driving instructors opt to join a large driving school franchise, the likes of aa, BSM or RED initially. Later, as they gain in confidence, driving instructors tend to either go independent and do their own marketing, or join smaller driving school franchises which usually provide better value for money. I'm with Drivecoach Driving School, a medium sized, driving instructor franchises and I'm really happy with the pupils and support they have provided me with.

I second that. Before the business, the logistics and the money decide whether or not the actual job is something you can genuinely do, and would enjoy doing. If so then you have the better foundations for success - work comes by word of mouth, and people hang on to a good instructor like a good tradesman/woman.

as an aside (and not directed at the OP) I feel the industry has been watered down, not helped by adverts everywhere you look claiming "become a driving instructor" "30k plus a year" "choose your hours..." This has lead to lots of people thinking "yeah I can drive" and "ooh loads a money," and results in a flood of people thinking they can just sit in a passenger seat and earn easy money.

Choosing your hours is rubbish. Ok you can choose when to work, ultimately, but most of the client base is going to be wanting lessons in daylight, so you're still on a 9-5 and later still working day. and to make it a full time living you will pretty much be needing to work many hours, but keeping pricing at a level that's both competitive and earning you a living. 30k is possible, but when you reach a self employed level, then take off insurances, maintenance (clutch changes!), fuel, expenses, advertising to start with, it soon drops...