Most instructors require payment especially those who teach for an IR. If payment is received for the purpose of the flight then it is Aerial Work. To conduct aerial work in a G reg aircraft the pilot must be appropriately qualified and the aircraft appropriately certificated.
I think S&L has picked up an important issue here. If you are commander and you pay someone else for their services in respect of the flight, the flight becomes aerial work. That means that the commander,
you in this case, needs a CPL.