An Utterly Impartial History of Britain is a rather irreverent romp through two thousand years of British history, collected under such diverse headings as "How the Romans eastablished our template for 'civilization' by killing anyone who didn't like it" and "How geography, religion and a spot of bad weather turned England into a major European power." Pretty much all of the major events in those two thousand years are at least touched upon in a faintly humourous fashion.
So why the low rating? This is for a few different reasons...
One of these is because O'Farrell's book doesn't really have an audience. Either you are a person who likes history - in which case, you would have read much more in-depth factual books about the periods that interest you - or you are a person who has little fascination in history and so this half-way house book wouldn't get your vote either. I believe that the only real audience is made up of people who quite enjoy John O'Farrell's newspaper columns and notice his name attached to this novel.
This on its own wouldn't be a problem, since it is more an issue of the commissioning of the book rather than the contents. It is just unfortunate that the contents suffer from being a little too glib. Actual facts are presented alongside anecdotal musings in the same fashion, leading someone unfamiliar with history to either believe all of it or none. As someone who has an interest in the reign of Henry VIII I felt that his misrepresentation of being syphilitic was unnecessary - the fact that none of his six wives or his mistresses or his children contracted the disease really gives the lie to something that O'Farrell presents as bald fact.
My other complaint is that O'Farrell believes he is funnier than he is. His 'amusing' analogies comparing historical events with modern day popular culture become boring and over-used. This, for instance, is a good example: "Various stand-up comics reminisced at length in 'I Love 1383' - 'God, the late Middle Ages; what was that about? Do you remember how there was always a squealing pig running down a muddy high street?' ...etc"
The one redeeming feature of the book is the gravitas and reverence with which O'Farrell deals with the two World Wars. Passages such as: "The Second World War has acquired a unique and hallowed place in British History, not purely because the war itself turned out to be so just, but also because of the extraordinary heroism of the servicemen and civilians caught up in it" make you proud to be British.
All in all, when O'Farrell is not trying to be self-consciously witty and clever, the book is an entertaining read packed full of little tidbits you might never have been aware of (such as where the Tory nickname came from). It is just a shame that he rarely reigns himself in.