The Unlicenced hop!
Public Transport dosn't specify cash but 'hire or reward'!
Take care. Someone must take benefit from the 'positioning flight' even if the student isn't charged cash.
Instructing is 'Arial Work' but the positioning legs may be construed as 'Public Transport' for 'hire or reward'. i.e. the Student as the passenger.
At the moment it would appear that no one wants to grasp that particular nettle, including the CAA, but it would only need an accident or a serious incident for the proverbial to hit the fan!