Literary feuds have drawn in such great writers as Keats and Byron, Dickens and Thackeray. The spy novelist John le Carré has this week penned a robust reply to criticism from a figure not of literature but of the intelligence world that his fiction depicts. We publish it today. Sir Richard Dearlove, former head of MI6, claims that Le Carré’s work is “corrosive” and emblematic of “counter-intelligence nihilism”. In reply, Le Carré, who served in the intelligence services in the 1950s and 60s, archly notes Sir Richard’s willingness in office to disseminate flawed intelligence about Saddam Hussein’s mythical weapons of mass destruction.

Le Carré’s writings illuminate a vital truth. Democracies require defending for what they are, not for some utopian vision of what they might