Answer:
The major blind spot is the offside that is the passenger side. Mirrors used to be mounted at the front of the wing giving a wide view of dangers in that area. They were also convex enough to give a wide view. Mirrors are usually now door mounted and less convex meaning danger slightly away from the car in that area cannot be seen on the mirror. Also the driver has to move his sightline farther than for a wing mirror and may have a frontal collision in the fraction of a second he is looking in the mirror..
A less dangerous spot is to the rear particularly if the boot lid is horizontal. This makes it common to back into a low obstruction.
Hopefully the problem will be solved with the advent of cheap web type cameras, and proximity warnings.