John Bingham, the real-life inspiration for John le Carré's George Smiley

"Small, podgy, and at best middle-aged, he was by appearance one of London's meek who do not inherit the earth. His legs were short, his gait anything but agile, his dress costly, ill-fitting, and extremely wet." Not someone who would leave an impression if you passed him on the street. But then that's the point: to fade into the shadows. The character, of course, is George Smiley, the inimitable creation of spy novelist John le Carré. Le Carré's Smiley novels, saturated in ambiguity and treacherous dealings, perfectly captured the unease of the Cold War years in the West. Smiley may not have been the perfect spy, but he was the man for the hour. Over the years, le Carré (born David Cornwell) has unveiled the real-life models for his fictional creation. One was the Reverend Vivian Green, whom the young Cornwell met at public school in Dorset. (Green was also later Cornwell's tutor at Lincoln College, Oxford.) The other inspiration, John Bingham, had a direct connection to the world of secret intelligence. Bingham was an operative at MI5, and worked with le Carré briefly in the late 1950s. He mentored him, but their relationship was put to the test once le Carré's literary career took flight. Bingham's life is an inviting subject for a biographer. The son of an Anglo-Irish baron - his father was the 6th Baron Clanmorris - Bingham (1908-1988) joined the Security Service in 1940 after a spell on Fleet Street. An almost comically strait-laced figure - Cornwell dubbed him "le Carré", the square, the coinage then becoming part of the famous pen name - Bingham proved masterful at his craft, handling his agents with skill. He was a keen listener and stringent interrogator, possessed of both empathy and objectivity. He could coolly appraise a situation and manoeuvre himself out of a tight spot. Bingham also had a second career as a writer of crime thrillers, several of which have been republished. And he knew how to compartmentalise: so secretive was Bingham about his work that for many years his own literary agent did not know he worked for MI5. It's a surprise, then, that Michael Jago's biography of Bingham falls so flat. Jago is a diligent researcher, but a tepid writer. This is an account that's as strait-laced, traditional, and conventional as its subject. Separating the fact from fiction when writing about the clandestine services is a difficult task; but there is precious little texture or drama in what otherwise might have been an exciting life story. Bingham was highly capable and beloved by his agents. In his work for MI5, he played cat and mouse games with the Abwehr during the Second World War, as well as travelling throughout Britain to investigate allegations of activity by enemy agents. He kept tabs on Britain's communists during the Cold War. He tracked subversive elements in the arts world. In the early 1970s, he looked into right-wing plots against the Labour prime minister Harold Wilson. A conservative, Bingham saw in extremes of left and right threats to the established order. The chapters on Bingham's relationship with le Carré - whose 23rd novel, A Delicate Truth, will be published next month - are the book's most successful, and will surely be of interest to fans for the light they shed on evolution of Smiley Bingham, observes Jago, "was a resolute, self-confident defender of Britain's character". He was also "an avuncular figure, a man who took great pleasure in encouraging men younger than himself". These two dispositions were put to the test over the decades he knew le Carré.