It's difficult to know quite how to rate this book, as David Owen himself doesn't seem to have a particularly clear idea of what the main aim of his book is. The core of the work is his piece on a proposed 'hubris syndrome' that affects the judgement of certain people in positions of power, in this case Tony Blair and George W. Bush in the run-up to and handling of the Iraq War. Proposing a new psychological diagnosis is always controversial (as is removing or altering an existing one), but Owen doesn't even seem to be suggesting it's a psychological disorder, which makes one wonder why he bothers to devote so much time to it to begin with. The notion that power corrupts is hardly anything new or radical, nor is the notion that some people are more susceptible to the trappings of power than others. The whole thing becomes even harder to take seriously when one takes Owen's own personality into account, as anyone who has followed his political career over the decades knows that his actions in the 1980s were pretty intensely hubristic themselves.
The rest of the book, despite being added as padding, actually fares a bit better. The idea of how to safeguard against the impact of physical and mental illnesses on the decision-making abilities of world leaders, both democratically and undemocratically chosen, is obviously a matter of grave importance to literally the entire world, and there have been many cases over the past centuries where clearly incapacitated leaders took actions they may not have otherwise. Owen's evidence is a bit conflicting when it comes to the actual outcomes of concealed illnesses in leaders though--obviously a lot is dependent on the nature of the illness, as well as the nature of the leader and the support offered by others in the government and close to the leader. It's a psychological blow to the people to know that their elected heads of state deceive them about their health, but is it always necessary to divulge medical information if it hasn't been shown to affect the ability to govern? Given the ongoing stigma about mental health issues, despite how widespread it is among leaders in particular (estimates are that as many as 49% of US presidents and over 70% of British prime ministers may have had some degree of mental illness at some point in their lives), this seems a particularly sensitive area.
All in all, it's a weird hodge-podge of a book, and tends to be rather self-serving, but it still contains a decent overview on the case histories of past leaders (Eden, JFK, the Shah of Iran, Mitterand) and some interesting potential proposals for the future.