Aerial work includes flying instruction for which the pilot is numerated. It is also aerial work where valuable consideration is given specifically for flying instruction, even if the pilot receives no award"
I guess the fact you're getting hours in you're log book for free counts as valuable consideration.
Don't get me wrong I would prefer it if some one could convince me that I am incorrect.
CAP 371 hinders those of us flying on airlines from enjoying our instructor/examiner ratings.