Correct me if I am wrong; in Europe, psychology is a social science and must not have anything to do with illnesses, only therapy. Psychiatry deals with illnesses as someone has to finish his medical university and then specialize in psychiatry (that is something like 12 years of learning altogether). In most cases, psychologists cannot diagnose illness properly as they are not educated in that direction.
I highly doubt the knowledge of psychologists over psychiatrists.
* This is just an observation from the EU point of view.