What is a fully qualified instructor?
To teach driving, you must be DSA qualified. You need to pass a three part test including theory and practice, much like a driving test but much more exacting, and a third part which measures your skill at instruction. While you are allowed to teach driving for up to six months before completing part three of test, you are not considered fully qualified.
Worse still, many false instructors without any DSA certification at all provide unsafe, unregulated lessons every day, passing themselves off as legitimate instructors. More than 100 such illegal instructors have been arrested in London in the past four years (for more information, see http://www.bbc.co.uk/news/uk-24181643)