Homeguard,
The bit about the pilot not being contractually required to fly is in the ANO, article 130. In my copy it is (9) (b)
"provided that neither the pilot in command nor any other person who is carried is legally obliged, whether under a contract or otherwise, to be carried."
Otherwise it is AW.
Of course, I may have taken this out of context. Such is the ANO. Unless one reads the whole lot, memorises it, one cannot be sure there isn't another para elsewhere that applies.
Your "difference" seems a very fine piece of hair splitting. Do you have some reference for this? Maybe the CAA have issued some flyer clarifying this; they've published many of those. How can a pilot be contractually required to fly (i.e. his contract of employment says he must fly on company business if asked to do so) and not be paid for the "act" of flying?
Traditionally, PPLs have always flown on their own business. (Unless one rents the plane out, this is indeed a requirement if one is to get Revenue/C&E concessions for it as a business asset). But the pilot has the choice of driving, walking, flying, etc.