Martin, I think it applies if they are acting in a supervisory role up... so accompanying one on a course as a buddy marshall, might well do, running a shoot i'd say yes, just being near one on a shoot, no. (in my opinion)
Certainly organised training/coaching yes. And you should check that you are insured to coach and train anyway, because the insurance requirements are quite specific on that under some schemes. I raised this with informally with an NGB rep recently as to what the advice was between the difference between coaching/training and just giving advice, and it's a grey definition that seems to rely on the intent at the time as to the depth of contact... ie a few short words about how to hold a gun, advice... 10 mins to one side working through a position... instruction/coaching/training...
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep