In the UK a psychiatrist is a qualified doctor who is a treating doctor. They diagnose and report on actual diagnosis of mental illnesses, substance abuse etc. They do not usually deal with personality disorders which are not classed as mental illnesses. Personality disorders are the remit of psychologists, as are learning difficulties. There is overlapbetween specialisms in some areas, such as mental capacity. So, a psychiatrist would diagnose and treat bipolar disorder, addictions, psychopathy, schizophrenia. A psychologist would assess and diagnose things like BPD, narcissistic personality disorder, Histrionic personality disorder. A psychologist can also assess things like Autism and other ASD's.