It all turns on whether, by manipulating the controls of an aircraft, one is "acting as a pilot". ANO Article 50 prohibits anyone from acting as a pilot of an aircraft without holding a licence; Articles 52 and 53 then provide exemptions for solo and dual flying training respectively, both of which require the involvement of a person who holds a flying instructor qualification.
Since the CAA declines to commit itself on this, as on so much else these days, the meaning of "acting as a pilot" will probably only ever be determined in a court of law following an incident or accident. The opinion of individual pilots is pretty much worthless in this respect and so the arguments will doubtless continue.