1. In an impressive piece of academic detective work, Frederick S. Litten made strenuous efforts to ascertain Noulen’ identity, his contacts and what happened to him after his imprisonment. Frederick Litten, ‘The Noulens Affair’, The China Quarterly, 138 (1994), pp. 492–512. Alexander Millar has expanded on Litten’s work adding in new dimensions, such as the role played by the Kuo Chen-chang (Gu Shunzhang), the Chinese Communist defector, and Harry Steptoe, SIS’s representative in Shanghai. See Millar, ‘British Intelligence’, pp. 76–149.
2. Frederick Deakin and George Storry, The Case of Richard Sorge (London, 1966), pp. 84–94 devotes a chapter to the Noulens affair but contains some factual errors.
3. In 1931, Britain’s share of trade with China was less than 8% compared to more than 11% in 1913. In Hong Kong, that share had fallen from 30% to 17% in the same period. In 1930 the British Empire accounted for under one-third of China’s trade but in the late 1870s that figure had stood at 85%. See Peter Lowe, Britain in the Far East: A survey from 1819 to the present (London, 1981), pp. 116, pp. 134–35.
4. See Christopher Andrew, Secret Service: The Making of the British Intelligence Community (London, 1985), chapters 7, 9 & 10; Ibid., The Defence of the Realm: The Authorized History of MI5 (London, 2009), pp. 139–59;
5. and Keith Jeffery, MI6: The History of the Secret Intelligence Service, 1909–1949 (London, 2011), chapters 6–7.