Thank you both for your replies. I didn't realise that much of the basic flying is in SOPs, making my example somewhat unrealistic - I think you got the gist of what I was asking though. :-)
What about the Captain who wants to continue below DH without the required visual references? (Again, this may not even be a remote possibility in the age of SOPs, if so I apologise now!)
In my head it might go something like this?
F/O: "Approaching DH, not visual"
Captain: "Oh, let's just go another 100 feet and see what happens..."
F/O: "Captain, you MUST go around"...... "I have control."
With use of positive/assertive language, ie address him as 'Captain' and emphasis on the word 'MUST'..