Show me the regulation where it says that during the flight, only "a pilot" may handle the controls, or that somebody handling the controls is (for the purpose of the regulations) considered "the pilot". Either a generic rule or one that is specific for take-off and landing. I'd be most interested, but I have never come across such a rule.
It took me a while but....
I can't find anything in EASA Part-FCL that defines pilot, passenger or handling the controls.
I can't find anything in the CAA ANO that defines pilot, passenger or handling the controls.
But there is a definition of pilot in ICAO ANNEX I chapter 1.1=
"Pilot (to). To manipulate the flight controls of an aircraft during flight time."
Article 50 within Section 1 part 6 of the ANO states:
"....person must not act as a pilot of an EASA aircraft that is registered in the United Kingdom without holding an appropriate licence granted, converted or rendered valid under the EASA Aircrew Regulation........"
It also covers being a student and none EASA aircraft later in the text!
Hope that helps!