indeed.my mate who's an instructor and been doing the job for 'years', had to go back to his HGV skills to keep afloat.. ( this was about 2yrs ago and he's kept the hgv up , doing nights on fridays and saturdays
)...to be fair, he probably used to get about 30k, though really only if you consider all the 'savings' a self-employed person can make.... but once the lessons dropped off his earnings flatlined... ( this wasnt RED of course)...
he also not only has to have the examiners test him ( i assume the 4 yrs thing?), but he's sometimes had the examiners examiner in the car as well.. so 4 people ... glad I wasnt the student at the time!!