BOAC
It is, no doubt, probably over-simplifying the issue here, but a captain cannot 'refuse' to operate into discretion.
N_N, just be very careful with your reasons 2 and 3, or I think your wonderful career (and pension prospects ) will be threatened.
Sorry old bean but I did read your post very carefully.
You say you are probably over simplifying the issue - on the contrary you are over complicating it.
The whole point with reference to the second quote above is that you don't have to give anybody any reason for refusing, just say politely.......' I'm sorry but I am not prepared to exercise my discretion to extend the duty'
If they persist just ask them to show you where is says you have to explain your decision - quite simply you don't!
You may read this as an unreasonable attitude, but believe me I have worked for a company which rapidly lost me my health as a result of appalling rostering. We have precious few weapons with which to defend ourselves as it is, so I feel very strongly about defending the few rights we still have.
Put it this way if Balpa can't kick this quickly into touch I ask you what can they defend?