When I was asked to review the long-anticipated memoirs of Theresa May’s former special adviser, Gavin Barwell, I originally felt a sense of dread. According to the blurb, in Chief of Staff, Barwell offers an “unflinching account of the tumultuous years” of Downing Street’s forlorn attempts to negotiate Brexit. For two years, Barwell had a front-row seat during one of the most dispiriting moments in modern British history.