Gordon Brown has been branded a "disgruntled dour Scot" who most voters see as uncaring.
The damning comments came in a book by former Labour First Minister of Scotland Henry McLeish.
Psychologist Anne Ellis also claimed that the Prime Minister's personality "just does not cut the mustard in popularity stakes" and warned he may lose the next election to a "much more pleasant personality".
She made the remarks in a profile of Mr Brown contained in a new book by Mr McLeish looking at Scotland and Scots.
Scotland - A Suitable Case for Treatment, was written by the former First Minister along with commentator Tom Brown, with a contributing chapter from Ms Ellis - a founder of the psychological profiling company PeopleMaps.
In it she suggested Mr Brown could learn a lesson from the current Scottish First Minister Alex Salmond, who she describes as "a consummate politician if ever there was one".
Ms Ellis says Mr Brown is "a very typical example of a dour Scot" and adds: "He has no time nor interest in courting popularity as he wants to get on with solving the problems of the world. What he has failed to see is that in today's terms the role of politician, due to media attention, is more a public relations job than any other."
In contrast she describes Mr Salmond, the SNP leader, as being "really gifted in telling people what they want to hear, always putting a positive spin even on bad news".
The book also says that in the eyes of the world Scotland is regarded as "dour" and argues that "the Scottish character must change to survive, never mind succeed, in the increasingly competitive future".
Speaking about the book in Edinburgh Mr McLeish said: "What we tried to do was to start with the assumption Scotland is a country of great talent, great wealth and huge potential. But it is our basic premise that that is not yet being realised to the full."
