Looks like I have been driving for 10+ years with my wing mirrors in the wrong position. My driving instructor, who was excellent in every other way, taught me to adjust my mirrors so I could see the side of my car. Turns out this is completely wrong, it duplicates most of the information already visible in the rear view mirror.
I can't believe it took me this long to realise.
http://www.linquist.net/motorsports/articles/mirrors
The only part I think is wrong is that there is no need to move your head around when adjusting the side mirrors. Just stay in your driving position and move them outward until the picture in the side mirrors overlaps only very slightly in the edges of the rear view mirror.