On the Blame Someone else tack....
My Dad (not actually diagnosed but some memory and cognitive loss) had two near misses and his car was written off in an accident. I said to him, unless you can deal with all the other loonies on the road these days (a very popular rant with him) then perhaps you should give up. Funnily enough the decision was easier because of this. He avoids the anxiety and stress of dealing with everyone elses terrible driving and we don't refer to his ability (or otherwise) to drive.
It was the right thing to do as he only drive in daylight, certain routes, in good weather......the list of things he struggled with grew and it just wasn't practical or safe any more.
Hi Helly68, I did exactly the same as this with my dad, he complained so much about other drivers, that I managed to convince him he was better off not driving due to all the other 'rubbish' 'loony' drivers on the road. I did also take his keys away from him, just in case he forgot this, until I could sell his car.
After this I just reiterated it whenever we were out in my car, only occasionally after that did he say he wanted to buy a new car, but I just either said we would at some time or I just ignored him.