There are 3 parts to the qualifying process to become a Driving Instructor.

When you have been accepted to start the qualifying process by the DVSA (Driver and Vehicle Standards Agency), you can start your training towards the three qualifying exams. These are known as:

Part One: Theory Test

Part Two: Practical Driving Test 

Part Three: Instructional Ability Test

You have to pass the tests in this order, and the part 2 & 3 tests have to be passed within a two-year period from when you passed part 1. Once these are all completed, you can then join the ADI register as an Approved Driving Instructor.