Even if he is an unpaid trainee then you do neeed the insurance upgraded otherwise you are not covered if he floods Lady Watsit's kensington pad.
Nor are you covered if you tell him not to touch anything while you go to the washroom and then he tests the chainsaw on his foot!
Its very time consuming having trainees. I only take adults and because I am so selective I can say that I have had some very good ones, some of which post on here. Those who telephone, if they cannot speak reasonably understandably, have no chance.
Tony