Before flight the decision must be made as to who is pilot in command ( the ANO requires it)........i.e. where two pilot fly together one must be designated as the commander.
That's only the case for a public transport flight. While I would be the first to suggest that the ANO would be better for requiring a commander to be designated for all flights, it offers only:
'Commander' in relation to an aircraft means the member of the flight crew
designated as commander of that aircraft by the operator, or, failing such a person,
the person who is for the time being the pilot in command of the aircraft;