Simple, straightforward lads who grow up to be worthy, industrious, selfless and decent citizens are no more likely to make it to the White House or Downing Street than they are to the Kremlin.

Their parents often have to console themselves that the perfect gentleman at 6 is a nonentity at 60. Everyone has heard the stories of Sir Winston Churchill's depressed moods, his love of excitement, his times of despondency and his periods of hyperdynamic, frenetic energy. The unhappy aspects of his childhood are part of history, as is his failure to thrive academically at school, despite a keen intelligence. But who now remembers, or has ever known, that Winston Churchill stabbed another boy at his prep school? I examined the scars on the hand of an elderly parson who had fended off the knife. Was this a manifestation of misery at having been almost abandoned by his parents, or was it an early symptom of the bipolar manic depressive personality that later won the war?

Anthony Eden's personality may not have fitted him to be Prime Minister, but it made him a brave soldier, a good scholar and a first-class foreign secretary. He probably behaved as a perfect gentleman at 6 but at nearly 60 when he became prime minister, he couldn't stand the strain.

Cracks in Eden's personality reached significant levels when he had to deal with the Suez Crisis and the party political schisms that this uncovered. Party dissention and the sudden loss of his lifelong hero status was too much for a decent, straightforward man.

Lord Owen, former Foreign Secretary, party leader and physician, has recently written on the health, or lack of it, of heads of government between 1901 and 2007. Owen quotes many examples of leaders whose behaviour supports the premise of the Ancient Greeks that there is a price to be paid by heroes who win glory and power by overcoming apparently insurmountable hurdles to reach the top. The already slightly aberrant personality of potential leaders is further distor- ted by success so that they become excessively self-confident and mistakenly believe that they are always right and capable of anything.

Reality has become blurred and the resulting lack of insight is unaffected by those around them as they have become increasingly separated from their supporters.

Owen ascribes many leaders' downfalls to the acquisition of hubris (arrogant pride and presumption) and the nemesis that this induces. It could be that Owen, and probably the classicists of old, overrate the importance of the hubris/nemesis cycle and underrate the influence on this cycle of the personality disorders and occasionally actual psychiatric disease that have encouraged potential leaders to enter the political ring.

The first evidence of this is often apparent in childhood and adolescence and to understand the importance of personality disorders political observers should hone up their knowledge of psychology. They should study the DSM4, the international index that lays down the important symptoms that are the hallmarks of the different conditions.

To some extent searching for clues in the DSM4, or stirring memories of long-past outpatient clinics, is a ticking-the-box style diagnosis. However it is interesting that Tony Blair, charming and charismatic as he is, scores a full house of ticks for a histrionic personality disorder, and scores in the boxes of a few other personality disorders too.

Gordon Brown has a personality forged in a Presbyterian manse and must have been influenced by its industrious, focused, perfectionist meritocratic ethos. When leaders crack because of stress they crack down predetermined fault lines. Many people with personality disorders excel in their career just because of these characteristics but when stress intervenes, the person with the personality disorder may become a patient with a psychosis.

Gordon Brown's personality, like at least 3 per cent of the population, shows symptoms of the personality disorders grouped together in DSM4 as cluster A disorders. He is likely to be demanding, self- absorbed, have difficulties in relationships with others, suffer discomfort in social situations with unfamiliar people, have vaguely unsettling inappropriate gestures or facial expressions and may be so focused that he finds it difficult to concentrate on subjects other than that which has caught his immediate attention.

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