I just reread this as part of an ebook binge on the long journey back from Melbourne to London.
I'd forgotten the quiet nastiness of the story- the rot disguised by the buffoonery. I think that's perhaps the most interesting thing about the way that it's dated, both for good and ill. Certain elements of Boris's public persona are the same as they were in 2013, and others have changed quite radically.
I think one thing that was true at the time which informs the book quite strongly was just how much Boris wanted to be liked. That old idea of 'Classic Boris!', the knowing clown winking at the public no longer quite rings precisely true.
I mean, elements of that persona remain- look at the Love, Actually ad in the campaign- but I think that one thing that the authors (and, in fairness, pretty much everyone else) failed to predict is that Johnson would quite happily embrace the hard, nativist right of the party rather than trying to circumvent them. One thing the book gets bang on the money is the role of shows like Have I Got Tired Jokes For You in normalising the man, but when it came down to it the Boris we have is perfectly happy to intimidate and attack the media rather than seek its approval.
Also, the book absolutely called that Labour was about to spend years in opposition as ineffectual, ideologically bankrupt incompetents. It just got the nature of that incompetence wrong.