Thanks lemongirl, your words really help especially about it being his choice.
I know he is in pain and I always moderate my conversations with him and my thinking to take into account that he is an old man living on his own who has lost his wife but his thoughts are pretty much for himself. I havent heard him express any real grief over the loss of my mum and even on the day she died, we travelled half way round the world, drove from the airport to pick him, take him to hospital to see mum and he then made us leave after a very short time because he wanted to get home, presumably to drink. We were so exhausted and jet lagged after 3 flights, nearly two days of non stop travelling and hours of driving him back and forth that we didn't return straight to the hospital and my mum passed away shortly after when I wasn't there.
I am going to be facing the same scenario with my dad fairly soon I think and want to do things better, try and help while I still can but don't know how. I can't even have anything approaching an honest conversation with him for fear of sending him over the edge. Assuming he is sober enough to listen. The only time we can relax a bit is when he has had another fall and is in hospital.
Some days I feel like the worst daughter in the world because I am leaving him to die horribly and others I would cheerfully smother him in his sleep.