Easily the most pervasive and dangerous of all the modern conspiracy theories is the one claiming that President George W. Bush and British Prime Minister Tony Blair knew that there were no weapons of mass destruction in Iraq before nevertheless deciding to invade in 2003. No other misrepresentation in recent times has so damaged the trust between government and the governed. How gratifying, therefore, that as authoritative and respected a commentator as Gordon Corera explodes that myth completely in "The Art of Betrayal," a wide-ranging, thought-provoking and highly readable history of Britain's postwar Secret...