The reference to JAR-FCL 1.010 quoted by Ryan5252, apart from not being UK law,
Not wishing to be pedantic but why isn't this UK law considering this extract from JAR-FCL is quoted in Lassors?
is irrelevant as simply handling the controls does not automatically make one a 'flight crew member'.
Nor did anyone assert that by 'simply handling the controls' makes one a 'flight crew member' as we all know it does not. But, by
operating the controls one is
acting as a flight crew member which is where the exclusion applies if said person does not hold the appropriate licence/rating.
The only considerations are the insurance requirements
The above example would be an insurance requirement.